After herding, the guard dog is perhaps one of the oldest canine professions. Traditionally, guard dogs were bred to watch over livestock, and chase down predators in the area. These dogs had to be fast, intelligent and strong. Molosser and Mastiff type breeds are broad terms which refer to large dogs bred by the ancient Greeks, Romans and Celts for the purposes of guarding territory and livestock. Many of today’s most effective guard dogs share a common ancestry in the Molosser and Mastiff, and retain their strong build, intelligence, and territorial instincts. It is important to consider that while many smaller dogs have strong territorial characteristics, they often make better watch dogs than guard dogs in that they might bark, but lack the strength and skill to effectively stop an intruder. A true guard dog can be trained to know when and how to attack and disarm an opponent.

The ways in which dog breeds find their way into guarding roles is perhaps as varied as the breeds themselves. Some ancient breeds, such as the Rottweiler, were originally bred for herding, but adapted into guarding roles through the need to protect livestock. Others, such as the Tibetan Mastiff, were bred and trained to guard sacred religious locations for as long as history has recorded them. More modern breeds, such as the Doberman Pinscher, have been bred exclusively as guard dogs in the past century. Amazingly, other modern breeds who were bred as herding dogs, such as the German Shepherd, have adapted into a wide variety of other roles, including that of a guard dog, in only a few decades. Other breeds commonly used as guard dogs today include the Belgian Malinois, the American Bulldog, the Pit Bull Terrier, and the Bullmastiff.