Territoriality in dogs is a behavior trait passed down from their closest relative, the wolf, and other wild canines. Most dogs are territorial to some degree, and it's not limited to males. Having two males who are aggressively territorial, however, can prove to be challenging.
In the Wild
In the wild, canines such as wolves will mark their territories by spraying a strong-smelling urine around the perimeter. This marking keeps other wolves away from the pack's territory, but in some cases another wolf will try to move in. Fights ensue over the territory in some cases, sometimes resulting in the death of a pack member or the new wolf. The territory is so valuable to a wolf pack that protecting it is a life-and-death matter.
Pet dogs normally display their territorial behaviors in a variety of ways, many of them not particularly aggressive. Marking the yard is common in both male and female dogs. Urine marking lets other dogs know the presence of the marking dog and can serve as a warning for passersby to stay away. Dogs will also bark and protect their territory and their family. The territory may be the yard or the home, but a dog who's walked around the neighborhood may see the whole neighborhood as his territory.
Difference Between Dominance and Territorial Aggression
While both dominance and territorial aggression are displayed in similar manners, there is a difference. If the two males are living in the same house, they may be actively trying to prove who is dominant over the other even though both accept the territory as shared. Wild canine packs have a social hierarchy with the alpha male and female at the top. Everyone else in the pack is lower than them, and the alphas get first pick on everything. Many dogs display this same sort of behavior to find the social hierarchy within their family group or with those who live close by. This can lead to problems and devastating fights. Dominance aggression is more common in male dogs than females and more common in purebreds than mixed breeds, according to the ASPCA.
Unfortunately, there is no one treatment to prevent dominance or territorial aggression tendencies between two dogs. Behavior experts have many different theories and the topic is widely debated. Neutering intact males could help curb some of the aggressive tendencies. Before consulting a behaviorist for your pup's aggression, have your veterinarian check him out to make sure there isn't an underlying medical issue behind the aggression. In some cases, dietary changes can reduce aggression.