If the approaching dog just stares at your dog and your dog goes for his throat, refusing to let go even when the other dog is whimpering and has rolled over, your dog is not behaving appropriately. Most interdog aggression occurs between housemates, and it occurs more commonly between same sex housemates. It is not unusual for two dogs to have lived together harmoniously for years before there are problems. The development of these problems reflects the intrinsic change that all social animals experience when they become socially mature. The more common of the scenarios for interdog aggression within households involves the younger dog, who was fine as a puppy, but now that he or she is becoming socially mature, challenges to the older dog have become more common.
Challenges can involve staring, vocalizing or outright aggression.
They can start with staring and escalate to aggression. Regardless, it is important to treat the problem as soon as it becomes apparent. The longer that it is allowed to persist, the worse the dogs will get. A similar scenario can occur even if the younger dog is not challenging the older. In such cases, it is the older dog that begins to sense the change in the younger and spontaneously starts to react to him or her.