hrmmm
You will get some good advice, but probably not all of it will agree. The point is that you should be able to do anything to your dog at any time, and that he/she should accept it with out growling, and with a cheerful heart.
Some people say that it's not dominant behavior, but I believe it is. I think that is your dog telling you, "You are not the boss of me! This is my bone, and I don't care what you want, you can't have it!"
IMO, that message is pretty clear. Here is an interesting article for you:
Is Your Dog Or Cat Possessive-Aggressive?
by Corey & Phyllis Cohen
Many people complain that their dog or cat guards his food or toys. We also hear complaints that their pet will guard their favorite sleeping or resting place as well. These problems can be serious if not addressed properly. Unfortunately, many people attempt the wrong approach to solving these problems. They often unintentionally perpetuate them as well.
When people get a new pet, especially a puppy, they often heed advice to show their pet that it's okay for them to approach his food bowl, or remove a toy from his mouth. They believe that every time the puppy is eating, it is a good thing to go over and take away the bowl for a moment, just to prove to the animal they can! They will attempt the same tactic with a toy, by approaching the puppy that is quietly chewing on his bone, and take the bone away. Of course, they always give the bone back, but the damage has already been done.
This approach will surely create possessiveness in the animal, as he becomes more and more fearful of someone taking away his stuff. Eventually, he hits his threshold, and fights back. Often he will only give you a warning growl, but often the dog will lash out with a bite. These bites can be very serious. This in turn causes the owner to either become frightened of the pet, or extremely angry. If they are afraid, the pet will sense this and feel as if he now has a way of gaining control of situations by acting aggressively. He will apply this strategy to other situations, because it was perceived to be effective. This evolves in to an aggressive, and sometimes dangerous pet.
If the owner becomes angry at the pet for growling or biting, then he may attempt to correct the animal. This makes the dog even more defensive, as he feels he needs to fight back to survive. The problem snowballs in the wrong direction. The dog or cat will begin to be afraid any time the owner approaches, and may act aggressively. This animal is often labeled a "fear-biter".
If you look at it from the animal's perspective, it is easy to see why this happens. Your dog is happily chewing his bone, or eating his food, and all of a sudden, for no reason, you come over and take it away. The first time this happens, it isn't a big deal, but after a few times, it becomes annoying. And after a few more times, it becomes an aggressive act toward the pet. You are doing to your pet the very thing you are trying to prevent him from doing.
Imagine that you are walking down the street, and someone grabs your handbag away. They immediately give it back and give you a compliment. A few moments later, or even the next day, they do it again. Day after day, this happens. Each day you grow more and more wary of people approaching you, and when you see the guy who keeps doing this to you, you grab on to your bag with all your might. There will certainly come a time where you will fight back, because you've decided that enough is enough! This is exactly how your dog or cat feels.
There is a better way to prevent and correct possessive aggression. It is best done preventively, but it is also quite effective as a corrective measure. Create a scenario where your pet actually loves when you take something away from them. He will invite you to come over and share their food bowl! He may even bring his possessions to you, rather than hiding from you in fear of losing them.
To begin, wait until your dog's feeding time. In his bowl, only put in half the amount of food he normally eats. The other half is either in your hand, or in a small bowl you'll hold on to. Put his food down and stand next to him. As he begins to eat, get his attention by calling his name, or making a strange sound. As he looks up at you, praise him, and offer him a small amount of food from your hand. Keep praising him as he eats this, and then let him go back to his own bowl. Repeat this process several times until you have no food left in your hand. Then let him finish his food. Repeat this process for one more feeding.
The next step is similar, but instead of standing next to him while he's eating, you'll walk up to him to put food in his bowl, and then walk away. Each time you feed him, you'll walk up to him. Do this for the next two or three feedings.
The next step is the same, except, put the food in his bowl, so he sees that you are adding food to his dish. Do this a few times during his feeding, and for three or four feedings. By this time, he should welcome you any time you come near his dish when he's eating. To maintain this, once or twice a week, while he's eating his usual portion of food, walk up to him and put a special treat in his bowl. You can even pick up his dish to add the treat.
A similar process is done for treating and preventing possessiveness of toys. Begin when your dog is happily chewing a bone, or playing with a toy. Stand next to him and begin praising him, so he feels no threat from you. Then, offer him one of his favorite treats from your hand. He'll have to drop the toy to get it, but make no attempt to pick it up. Repeat this a few times each session for a few days in a row.
The next step is to hold out your hand and ask your dog to "drop it", as you show him the treat. If he does, and eats the treat, immediately give him back his toy and praise him. If he won't let go, then gently take it out of his mouth, give him the treat, then the toy back, and praise him. Repeat a few times for a few days in a row.
To maintain this, once or twice a week, just go over to your dog when he's playing or chewing, offer him a treat for his toy, then give him the toy back with lots of praise.
This is all you need to do to get your dog to feel as if he benefits from you taking something out of his mouth, or going near his food. He will be eager to let objects go, because he is getting something in return. You will successfully increase his level of trust for you through these simple steps.
If your dog is possessive of locations, such as his favorite sofa, the same method will apply. Just approach him and offer him a treat the first few times. Then ask him to come off the sofa (or away from the location), for the treat. Maintain by doing this once or twice a week.
Many problems can be avoided by looking at it from your dog's perspective. Think of how he feels each time a certain event happens. Remember that the overall goal is to create and maintain a successful relationship with your dog, one that is based on trust and respect rather than deceit and intimidation.