Does your happy-go-lucky dog turn into Cujo when you attempt to take away his bone, toy or remove him from his favorite resting spot? In the training world we refer to these dogs as "resource guarders."
Resource guarding is natural behavior
While this behavior is totally unacceptable to humans, it's a natural and normal behavior in dogs. In order to survive, wolves have to protect their "stuff." The notion of sharing isn't part of the picture. Despite the fact that dogs have been domesticated for many years, innate behaviors still exist.
Training and management
Every dog and situation is different. If your dog only guards a specific resource, such as a rawhide, the solution may be as simple as eliminating rawhides. Some dogs only guard something they've stolen, like a tissue. Others guard a toy, but only if they've been chewing it for 15 minutes. Still others might only guard a coveted spot on the couch.
When you approach your dog and he has a coveted resource, in his mind you're there to take it away. Never mind the fact that you have no interest in the slimy rawhide that he is chewing. He goes straight to "Intruder Alert!" mode. This emotional response is what triggers all of the snarky behaviors that normally follow.
The protocol for changing Cujo into Lassie involves convincing your dog that when you approach him it's not because you want to take his "stuff." In fact, you want to give him something even better than what he has, like a piece of cheese. Over time, he'll go from "Intruder Alert" to "Oh yippie! Here she comes with treats!" Changing your dog's attitude about your intentions is important in eliminating resource guarding.
The training involved in reducing resource guarding can be tricky and should often be done with the assistance of a professional trainer or certified animal behaviorist. To learn more, an excellent book, entitled "Mine!" by Jean Donaldson, provides great insight into why dogs guard and includes extensive instructions.