1Akita
Getty Images Akitas have a large build (just look at the size of that head!) which makes them a powerful animal. If you socialize them well with family and friends early on in life, they'll know who's a playmate and who's an intruder.
RELATED: 22 Healthiest Dog Breeds With the Least Health Problems
2Appenzeller Sennenhund
Getty Images Though smaller than some of the other large dogs on our list, Appenzeller Sennenhunds still make a great guard dog due to their agility and energy. They were originally bred to work as farm dogs, so their intelligence and obedience can do double duty if you've got some land.
3Australian Shepherd
Jeff Greenough//Getty Images The medium-sized Aussie is both beautiful and brave. Most at home on a ranch or in a rodeo, these dogs are natural herders and will take any opportunity to get other animals (or even kids) in line. What's more, they make energetic playmates for the whole family.
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4Bullmastiff
Getty Images These large, muscular dogs are a cross between Bulldogs and Mastiffs in a super-size package. To avoid altercations with other animals or people, they're best suited for houses with fenced-in yards. Bullmastiffs are a great walking companion, but leave them at home when you go running, since they're not built for sustained speed.
5Catahoula Leopard Dog
Getty Images 6Caucasian Shepherd Dog
Elen11//Getty Images These massive pups know exactly how to respond if they sense a threat to your house or family members, so don't underestimate their disarming fluffiness. The Caucasian Shepherd dogs are a great option if you have older kids and other animals, because they're loving and careful around people they know and trust, as long as they're well-trained.
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7Chesapeake Bay Retrievers
LawrenceSawyer//Getty Images This powerful pup boasts a wavy, waterproof coat that sets it apart from other retrievers. However, you can still expect the loyal and energetic traits that make Golden Retrievers and labs one of the most popular pets. Chessies are polite with strangers, but still cautious and not overly affectionate with those they don't know — all of which makes them excellent watch dogs.
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8Doberman Pinscher
Getty Images Don't let a Doberman's sleek body fool you — they're strong, fast and fearless, making them the perfect dog to guard your house. The energetic breed requires a lot of exercise, so be prepared to go on long walks with them if you don't want to come home to a mess.
9Estrela Mountain Dogs
studiof22byricardorocha//Getty Images Estrelas are thought to be one of the oldest breeds in Portugal, where these dogs are named after a range of mountains. They're super gentle and protective of their people, so they'll fit in with a tight-knit family.
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10German Shepherd
Getty Images German Shepherds are one of the most common breeds for police dogs, but they're just as popular as pets. They'll protect your house from intruders and are so loyal that they will form a strong bond with you. If you're looking for a pup you can train to do just about anything, look no further.
11Giant Schnauzer
Getty Images The Giant Schnauzer is basically a stronger, larger version of its standard counterpart. Be prepared to spend a decent amount of time grooming them, because that thick coat of hair requires regular brushing — they've got a beard, after all!
12Puli
Bigandt_Photography//Getty Images Honestly, what better breed for a guard dog than one that can so easily go undercover as a mop? (The jury's still out on whether they will clean your floors for you, though.) Puli dogs were originally meant for herding, so they learn fast and can easily outsmart any predators. Their goofy appearance hides a super smart pup.
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13Romanian Mioritic Shepherd Dog
-massmedia-//Getty Images This type of guard dog bonds closely with its owner, so they won't do well if you leave them alone for long periods of time. Romanian Mioritic Shepherd dogs are loving and kind enough to be your closest bud, but they will bark and get aggressive if they encounter strangers they don't already know and trust.
14Rottweiler
Getty Images If you know anyone with a Rottweiler, chances are that you've experienced their gentle nature around their owners. But their standoffishness can be intimidating when it comes to strangers. To ensure they mind their manners, socialize your Rottie with other people and dogs in addition to taking them to training classes to make the most of that big ol' brain.
15Staffordshire Bull Terrier
Getty Images Not everyone has the space for a large animal in their home, but that doesn't mean they don't need a powerful guard dog. Generally weighing in at less than 40 pounds, Staffordshire Bull Terriers are muscular, brave and natural fighters when they need to be. They also have lots of energy, so long walks and plenty of playtime will keep them (and you!) in tip-top shape.
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