Some dogs know what they want and will be very aggressive about getting it. They'll bump against their owners to demand attention. They'll take over certain spots in the house and nothing will induce them to move. They will insist on playing or being petted and won't take no for an answer. Essentially, they want to call all the shots.

Aggression can take more serious forms as well. It's not uncommon for dogs to growl or grumble -- or in some cases, to bite -- in order to have their own way. This type of aggression never goes away on its own. In fact, it's the most common behavior problem that sends owners to behaviorists and trainers looking for help.

Aggression is a complex problem because it can be caused by many different things. Some dogs simply have dominant personalities. Even if they never show signs of actual aggression, they'll always try to get their way. Other dogs may be insecure or angry. They're the ones most likely to growl or bite. You can tell a lot about your dog's personality by the way she expresses her aggressive or dominant tendencies. Here's what the signals usually mean. "Hey, talk to me." It's fairly common for dogs to nudge or gently butt their owners simply because they want some attention. This type of behavior usually isn't a problem as long as dogs aren't acting pushy under other circumstances.

I want to be in control." Dogs that are always nudging people and who also play roughly, take over choice spots on the furniture, or refuse to move when their owners try to squeeze past are showing more serious forms of aggression. They want to be in charge, and they're taking steps to fortify their advantage. Unless you stop them quickly, they'll continue trying to be dominant and will get pushier and more difficult to be around.

Since biting, growling, and other forms of aggression can be quite dangerous -- not only to you, but to other people as well -- you may want to call a trainer for help. But the basic principles of "demoting" a dog and making her more cooperative aren't very difficult to apply.  For example, play games in which you and your dog cooperate, like throwing a ball or going for walks. Games such as tug-of-war, however, create a mood of competition, which only reinforces a dog's desire to come out on top.

Territory and possession can mean a lot to dogs, which is why aggressive behavior often includes taking over the furniture and refusing to move. As long as your dog is showing signs of aggression, you should keep her off the furniture all the time. Dogs see the furniture as a "choice" location, and by keeping them off, they'll come to understand that their position in the family is subordinate to yours.

Doorways are another form of territory, and you should make sure that your dog always goes through after you and not before. In addition, don't let her lounge in front of a doorway or a flight of stairs. Your dog should happily give way to you, not the other way around.

Taking your dog for long walks or doing regular obedience work are superb ways to control aggression. It strengthens the bond between you and reinforces your role as the leader. It also will tire her out, and a tired dog is less likely to be aggressive.

Let your dog know there's no such thing as a free lunch, that it's her job to earn your attention. Don't give her anything -- food, petting, or anything else -- unless she does something for you first. Make her sit before going outside, or practice other commands before putting her food on the floor.