Territorial aggression is not only expressed toward another dog but can also be expressed toward people. The dog attempts to protect his resources, mates and offspring against infiltrators and potential usurpers. The territory generally includes the house and yard plus abutting areas (e.g. sidewalks) that the dog regularly patrols and any family vehicles in which he routinely rides. When dogs show excessive territorial behavior only on their perceived property, but do not respond aggressively to strangers in neutral territory, territorial aggression is the likely diagnosis. There are two primary motivations for territorial behavior, dominance or fear.
For more information, please read Territorial Aggression Toward People