Aggression is an unfortunate tendency that now occurs across all breeds and breed mixes. A dog doesn't have to launch a full-blown attack to exhibit aggression. Issuing a warning growl, curling a lip to show teeth, snarling, and biting are all acts of aggression. However, do not get caught up in all the references to dominance and alpha in dog literature. A dog exhibiting aggression is not automatically bent on taking over the household. In fact, fear aggression is more common than dominance aggression.
Don't assume you don't have to worry about aggression simply because your dog is so small. There are households in which people are afraid to move around their aggressive Yorkie. Aggression is not acceptable no matter what size the dog may be and action must be taken to eliminate all aggressive behavior.
Types of Aggression
Aggression can arise out of many circumstances, some less troublesome than others. Maternal aggression that only occurs when a mother has pups is not a major problem. The mother can be lured away from the nest with her food bowl or treats when the puppies need to be handled. (Though perhaps this mother should not be bred again, as nervous mothers can create nervous puppies.) The problem becomes more serious if the female starts exhibiting protective behavior over stuffed toys or other surrogate puppies.
As mentioned, fear is the most common basis of aggression. In human society, frightened dogs often aren't free to just run away. So they default to their second option: warning the scary thing to stay away. Frightened dogs would rather avoid the conflict, but if cornered they may feel that they are fighting for their lives. They are quite likely to bite if pushed.
Possession aggression occurs because canine rules differ from human rules when it comes to owning things. Even low-ranking members of canine packs own some object that is in their possession, and fights are rare. To be constantly fighting over scraps of food would be counterproductive to the pack's survival. Yet humans expect their dogs to willingly give up possessions to them. It doesn't happen automatically.
Dealing with Aggression
No form of aggression should be tolerated, but responses to the different underlying causes indicate different solutions. For example, if snarling or snapping arises suddenly, a visit to the veterinarian is in order. The sudden aggression may be in response to pain from an injury or illness.
Never punish a dog for growling. First, aggression by you (punishment can be viewed as aggression) begets more aggression, so you're making the problem worse. Second, growling is a warning, and if you eliminate the growling without correcting the underlying problem, you may create a dog that bites without warning.
Photograph by Jean Fogle
Curb aggression early to prevent unmanageable problems later on.
To avoid possession aggression, convince your dog that giving things to you results in receiving even better things. While your dog is eating, drop an extra-special treat in the bowl. Gradually bring your hand closer to the bowl to drop the treat, until you are actually placing the treat in the bowl.
Also do trades for toys, having a second toy of equal or greater value than the one the dog has, and making it more interesting by showcasing your interaction with it. While you are working on possession aggression, keep human-valued objects such as the remote control safely out of reach of the dog, or at least tie a long string to them so you can get them back without confrontation.
Unfortunately, board-certified veterinary behaviorists are rare in the United States. They number only in the few dozens. However, many trainers educate themselves remarkably well. Be sure to ask your trainer about his experience in dealing with aggression.
Fear aggression can largely be avoided with proper socialization. Be sure your young Yorkie meets other people of all shapes and sizes and other dogs (in safe conditions), and encounters bicycles, school buses, park benches, mirrors, elevators, roller skaters, horses, and other possibly distressing stimuli. Make a game of it — try to introduce your dog to five new people or things every week.
If you've rescued an older Yorkie, or neglected this early socialization and now have a dog with fear issues, or you think you have a truly dominant-aggressive dog, you need face-to-face help from a trainer or behaviorist skilled in such problems. Look for someone who will use positive reinforcement with what is called classical conditioning — associating a good thing with the scary thing over and over.