Territorial aggression is a potentially dangerous behavior problem. In mild form, dogs bark to intimidate intruders, particularly those of the same species. The barking is also intended to alert other pack members who can join in defense of the pack's territory. If the intruder is not intimidated, warnings may escalate to include hostile posturing and lunging. And if this is ineffective in deterring the visitor, an attack may ensue.

Although alarm barking can sometimes be aggravating for dog owners, neighbors, and visitors, lunging and biting are far more serious problems. Dogs with the confidence to bite strangers present a danger to any visitors to the home and a liability for the dog's owners.

By definition, territorial aggression should be expressed toward members of the same species. Domestic dogs, however, seem to regard people as conspecifics and consequently may direct territorial aggression toward human visitors. "The territory" generally includes the house and yard, plus abutting areas (e.g. sidewalks) that the dog patrols, and family vehicles in which he rides.

When dogs display aggression to strangers only on the home property, and do not respond aggressively to strangers on neutral territory, territorial aggression is the likely diagnosis. There are two primary motivations for territorial behavior, dominance or fear/anxiety.

Territorial Aggression Fueled by Dominance

Dominant dogs have a responsibility to warn other pack members of a stranger's approach and they do this with confidence and authority. Dogs that are overly dominant, both in absolute terms and with respect to their human family members, may provide a serious obstacle for any visitors to the home territory. Where owners have some control, they can usually reassure the dog that the person is, in fact, welcome, at which point the dog will settle down. In most cases, once a stranger has been welcomed inside the home, the dominant-territorial dog will relax and enjoy the visitor's company.

Territorial Aggression Associated with Fear

Some dogs, notoriously those of the herding breeds, show a variation of the territorial aggression theme. Perhaps they do possess a low level of dominance and would bark anyway, but some are also insecure, anxious, or even frankly fearful. As youngsters, they may back up and bark at the sound of people approaching but, as they grow older, they find themselves more intimidating and learn that they can drive the bogeyman away. Uniformed visitors, like the mail carriers, are prime targets for this learned type of aggression. The mail carrier comes, the dog barks, the mail carrier leaves, and the dog takes credit. The aggressive behavior is thus reinforced. Out on the street, these same dogs may not have the courage to intimidate their adversaries, although they might wish they had.

There are several factors that distinguish fear-related territorial aggression from dominance-driven aggression:

Territorial/fear aggressive dogs frequently show ambivalent body language similar to that of purely fear aggressive dogs. The body language includes: approach-avoidance behavior, tucked or semi-tucked tail, slinking gait and an indirect approach.

Territorial/fear aggressive dogs do not usually settle down completely while visitors are in the home and are prone to sudden outbursts of barking or lunging and may aggress toward visors who move suddenly, speak loudly, or get up to leave the house.

The bites of territorial fear aggressive dogs are usually directed towards the "nether regions" of the offender (e.g. toward the person's buttocks, thighs, or calves) ... or they may simply nip, ripping clothing. The bite is usually of a hit-and-run nature – a cheap shot.

In a way, the only distinguishing feature between territorial fear aggression and overt fear aggression is the level of confidence that the dogs possess. Fear aggressive dogs generally have enough confidence to be aggressive to strangers on or off their own territory. Territorial/fear aggressive dogs have a lower level of confidence that permits the expression of fear aggression only on the home territory or from within the safety of the owner's vehicle.