Possessive aggression occurs when the dog is defending a cherished object (toy, bone, food). Control of important resources is somewhat normal in dogs, but possessive aggression exceeds the tolerated limits of this behavior.
Territorial aggression is defensive behavior of a geographic area. Although it is normal for dogs to bark at strangers and other animals approaching their home turf, territorial aggression usually involves an unacceptable escalation of protective behaviors. Territorial aggression can involve small spaces (a favored resting place, a room, an automobile) or large ones (yards, farms).
Aggression in dogs is normal and to a certain level, appreciable. Dogs are bred to protect and at times it may be an issue of training and learned behavior. This behavior can be changed in some dogs but determining the underlying cause is important.
Symptoms and signs of possessive and territorial aggression include:
Lifting the upper lip
Extreme reaction when someone approaches the dog’s space (e.g., backyard)
Doorbell may bring on a frenzy of aggression