Directory

After being drafted by the National Football League and playing with the Dallas Cowboys and the San Diego Chargers, Sean Lissemore joined the St. Mark’s administrative team as athletic director in 2019. He earned his bachelor’s degree from the College of William and Mary and his master’s degree from Indiana University. A former collegiate football player at the College of William and Mary, he served as team captain and earned All-American honors. His professional football career consisted of 69 games, where he registered 135 tackles, 6.5 sacks per game, one interception and one touchdown over a seven year career as a defensive lineman. He founded and organized the Sean Lissemore Youth Football Camp, a free enrichment program for children in Dumont, N.J. and was named the San Diego Charger’s NFL Military Salute to Service nominee. He’s a member of the National Interscholastic Athletic Administrators Association and serves as eighth grade class adviser.

Mark Sullivan joined the St. Mark's School of Texas faculty in 1982 as the Lower School Physical Education Coordinator. Prior to his appointment as the Director of Athletics and Physical Education in 2000, Mark has served the school as the Wilderness Program Director, the Assistant Head of the Middle School and as a coach and teacher in the Athletic Department. Mark holds a Bachelor of Science Degree and a Masters Degree in Educational Administration from the University of North Texas, and is a recipient of the John H. Murrell Excellence in Teaching Award. Mark's coaching has included numerous Middle School sports as well as the Varsity Volleyball team and the Varsity Diving team.

After a distinguished career in the military, which included stints as a cannon crewman, a military intelligence officer and several tours in Iraq and Afghanistan, Reyno Arredondo ’87 returned to his alma mater in 2017 as head wrestling coach. He earned his Bachelor of Science degree from the United States Military Academy at West Point and a Master of Arts degree from the University of Texas at Austin. During his military career he taught in the Department of Foreign Languages and Behavioral Sciences and Leadership, as well as serving as an associate athletic director in the Directorate of College Athletics, Army-West Point. At St. Mark’s he is also a physical education teacher for Middle and Upper School students, seventh grade baseball coach, seventh grade adviser and sponsors the Martial Arts Club. He’s an inductee in the Texas Wrestling Hall of Honor and was awarded three Bronze Stars and earned Airborne and Air Assault wings during his military service.

With a distinctive voice familiar to Lion sports fans, Robert “Doc” Browning has been the announcer for varsity basketball games and lacrosse matches for decades. He’s a member of the Athletic Department, where he serves as athletic trainer and teaches Lower School physical education. “Doc” earned his Bachelor of Arts degree from North Carolina State University and served in the U.S. Army, with an honorable discharge in 1975. He previously served as head athletic trainer at Rhodes College in Memphis and is a nationally certified athletic trainer. Browning has been the recipient of the John H. Murrell Excellence in Teaching Award in 1994, the Ralph B. Rogers Alumni Award in 2007 and the Ackerman Character Education Award in 2015.

Natalie Bumpas has been a member of the School’s athletics staff since 2020 and currently serves as athletic trainer. She earned a bachelor’s degree from Indiana University and a Master of Arts degree from the University of Iowa. Before coming here, Bumpas served as an associate athletic trainer at Northwestern University and as an assistant athletic trainer at the University of Nebraska-Omaha. She also interned for the New York Mets during the 2011 season. Bumpas is nationally certified by the National Athletic Trainers’ Association (NATA) Board of Certification, and has been a member of NATA since 2004. She is also a licensed athletic trainer in the state of Texas and recently became certified in Graston Technique for soft tissue mobilization.

After playing football at Princeton University, Harry Flaherty spent brief stints with the New Orleans Saints, Tampa Bay Buccaneers and Dallas Cowboys before moving to the University of Tennessee, where he earned a law degree while coaching football in a graduate assistant role for the Volunteers’ football program. Coming to St. Mark’s in 2021, he now serves as head football coach, Upper School history teacher and adviser in the 11th and 12th grade rotations. Before joining St. Mark’s, Flaherty spent six years at The Lawrenceville School in New Jersey, where he served as a history teacher, head varsity football coach, assistant dean of Admission and housemaster for all ninth grade boarding boys.

Josh Friesen joined the St. Mark’s faculty in 1998 and currently serves as associate athletic director. He earned a bachelor’s degree from the University of Kansas and, after college graduation, worked at the Cooper Aerobics Center in 1997-1998 while coaching basketball and baseball part-time at St. Mark’s. The following year, 1998-1999, Friesen joined the St. Mark’s faculty full-time in the Athletic Department. Friesen serves as an eighth grade adviser, junior varsity volleyball coach, ninth grade basketball coach and eighth grade baseball coach. He received the Murrell Excellence in Teaching Award in 2013, the Senior Master Award in 2022 and was named Middle School Basketball Coach of the Year by the Texas Association of Basketball Coaches for the 2003-2004 season.

The varsity head basketball coach since 2006, Greg Guiler has the distinction of being the all-time leader in career wins among the School’s many storied athletic programs. He joined the St. Mark’s faculty in 2005 and currently serves as a teacher and coach in the Athletics Department, where he has also served as head golf coach since 2016. He has been a head coach in the lacrosse, baseball, and football programs at various sub-varsity levels and has taught physical education across the Lower, Middle and Upper and School divisions. Dad to Cooper ‘26, he earned a Bachelor of Arts degree from Cedarville University and a master’s degree in cross-cultural studies from the Dallas Theological Seminary. Guiler received the John H. Murrell Excellence in Teaching Award in 2013 and was named a finalist for the Ralph B. Rogers Alumni Award in 2011. The Texas Association of Basketball Coaches twice honored him as Coach of the Year (2007 and 2020) and he was named Texas private schools Most Outstanding Coach in 2013. His 2020-21 varsity basketball team was the first in the history of the Southwest Preparatory Conference to be ranked #1 among all schools in Texas and in the Top 25 nationally.

Cameron Hillier ’13 returned to his alma mater in 2020 as a member of the English Department, where he teaches classes in junior English, literature of war and survival and dystopian literature. Before returning to St. Mark’s, he earned a bachelor’s degree from Colby College. Hillier is the head tennis coach here, directs the School’s Wilderness Program and serves as an adviser in the freshman-sophomore class rotation. He also taught English at Christ School in Asheville, NC while coaching tennis and serving as head of house for one of the campus dormitories there.

Matt Hjertstedt has been a member of the St. Mark’s community since 2008 and serves as head athletic trainer in the Athletic Department, where he also teaches Middle School physical education and health classes. He earned his Bachelor of Science degree from Central Washington University and Master of Science degree from Texas Tech University Health Sciences Center. He’s also a certified athletic trainer and a licensed athletic trainer. Before joining St. Mark’s, Hjertstedt worked in the fitness industry as a personal trainer and strength coach. A dad to current Marksman Westin ‘31, he also spent time working at Harborview Medical Center in Seattle in the Acute Rehab Unit. Hjertstedt also sponsors an independent studies course in sports medicine for Upper School students and received the John H. Murrell Excellence in Teaching Award in 2014.

After a professional baseball career with the San Diego Padres farm team and the AAA Portland, Oregon Winterhawks, John Hunter came to St. Mark’s in 2008, where he currently serves as Middle School humanities teacher and head varsity baseball coach. Hunter earned his Master of Arts in Humanities degree from the University of Texas at Dallas and a bachelor’s degree in political science from Texas A&M University. After his baseball career, he transitioned to teaching and coaching, working at Arlington Martin High School and Keller High School before joining the Lions’ staff. Hunter is also the eighth grade class sponsor and eighth grade head soccer coach. A St. Mark’s parent (Blake ‘32) he received the Ackerman Character & Leadership Award in 2018.

A native of Cuba, Corindo Martin began his St. Mark’s career in 1990 teaching mathematics and coaching soccer in the Middle School. Now, he is head soccer coach, winning SPC championships in 2012, 2013 and 2020. Martin holds a bachelor’s degree in mathematical sciences from Southern Methodist University and gained valuable teaching experience while on a teaching fellowship in graduate school at the University of North Texas. He has been involved in youth soccer at both club and recreational levels before his arrival at St. Mark’s. An eighth grade class advisor, he received the Ralph B. Rogers Award in 2006. He’s the father of two Marksmen — Gabe ‘18 and Luke ‘22.

Whitney joined the Office of Development as Alumni Relations Coordinator in September 2020. She graduated from the University of Texas at Austin in May 2020, earning a Bachelor of Science in Physical Culture and Sports and a certificate in Food and Society. Whitney was a four-year member and Co-Captain of the University of Texas Cheerleading Squad, where she gained experience in community relations, event planning, and social media.

Dwight Phillips began his St. Mark’s career in 2000 as a member of the Physical Education Department. His previous teaching experience was at Greenhill School in Addison and at All-Saints School of Lubbock. Phillips received his undergraduate degree from Texas Tech University in exercise and sport sciences. While a Red Raider, he was a member of the varsity basketball team. In addition to his teaching duties, he coaches Middle School volleyball, basketball and track & field, and serves as an Upper School advisor. A towering figure on campus, Phillips was named recipient of the Ralph B. Rogers Alumni Award in 2014 and received the dedication of the Marksmen yearbook in 2022.

After a collegiate coaching career at Mary Hardin-Baylor University, Darren Teicher joined the St. Mark’s faculty in 2008 where he serves as head volleyball coach. He earned a bachelor of science degree from the University of Mary Hardin-Baylor, where he won a national championship as a player. As a coach here, his teams have won seven SPC volleyball championships.

After a collegiate coaching career, John Turek came to St. Mark’s in 1996, where he is head coach of the track and field program. He also was cross country head coach for 26 years here, and now assists with those athletes. He has a bachelor’s degree in criminal justice from California State University-Los Angeles and a master’s degree in physical education from California State UniversityFullerton. His collegiate coaching career includes cross country and track and field head coach at California State University-Los Angeles and physical education teacher, women’s cross country and track and field head coach at California State Polytechnic University-Pomona. He also serves as an advisor in the ninth and tenth grade class rotations.

A member of the Lion athletic staff since 1988, Ron Turner is the athletics equipment manager. He earned an associate of science degree from the Dallas County Community College District. He serves as Middle School tennis coach, scheduler for varsity and middle school tennis and has been a member of the Athletic Equipment Managers Association since 2001. Father to Chris ‘91, Turner was named recipient of the Booker Kilgore Award, recognizing him as the High School Equipment Manager of the Year, in 2022.