Guarding behavior is very normal for dogs. We humans don't like it much; although there are some people who think it's cute when their dog guards them. I was almost bitten when I was very young; we were at a cottage and the dog that lived there was chewing a bone. Having come from a very non dog family; I was never told to leave dogs alone when they were eating or chewing. I approached the dog to pet it; I got closer and closer where the dog would have obviously frozen, given me the lazer beam eyes and a display of his teeth. I didn't stop; as a child you don't see these warnings. The dog lunged at me and grazed my arm; he then ran back to his bone and threw me a couple more dagger stares.
Yes; he was guarding his bone. Some dogs never guard; some guard with dogs and not humans,there are all different levels of guarding. What factors in on the level of guarding is the value that an individual dog puts on an item. When a dog guards a human; they are claiming you, this is my girl or guy. And it is not cute; no matter how cute the dog doing it is. Guarding needs immediate attention no matter what level it is at.
My little Jack Russell showed right from the start that she was going to be a guarder. At 12 weeks of age she gave me quite the display of her tiny teeth when I tried to move her rawhide. That was nearly 14 years ago; and since then we have never had rawhides in the house. Reason one was Jessie; and two is that they are not good for dogs. And three is that I know of two dogs who actually choked to death on them. So with the rawhides gone we didn't have any problems; solved until the entry of raw bones. There we have a slight issue; but that has been solved as well which I will explain a little later.
The approach of many to a guarder is "oh ya? I'll take whatever I want." So; often people snatch the food bowl away from their dog, or the bone or toy or whatever they are guarding. Now think for a minute. The dog is guarding because they think that you want their stuff; which you pretty much just proved correct. What we need to do is teach them that we don't want their stuff most of the time; but if we did want it, that is a good thing.
What I do with Jessie and raw bones is trade and offer good stuff for any approach. So she is outside with the other dogs chewing; I will walk up to her and offer her a piece of raw beef which I cut off the bone before giving it to her. I do this with my poodles as well. What this does is make my approach a good one; instead of a negative one. I also trade bones; I take out a plate and tongs (meaty bones that are already chewed are pretty gross). I pick up Tilleys first and put it on the plate; bring it over to Jessie. Jessie drops her bone to see what I have and I give her Tilley's; picking up her bone. I then bring Jessie's to Luke and give Luke's to Tilley. This is another exercise in "my approaching is a great thing."
Many place guarders can be managed by taking their "place" away. If a dog has issues while in a certain bed; the easiest option may be to get rid of the bed. But some dogs will just choose another spot to guard.....so for these guys you use the "approach is good" routine. Depending on the level of guarding that your dog is showing will factor in on how long it should take to get rid of. Some dogs turn around quickly; others are diehard guarders unwilling to let it go without a fight. Baby steps are the best line of approach when dealing with guarders.
So whatever the object of the guarder is; you need to convince them that having people around it is a great thing. Management is the first step and then the work should begin. The goal of the work is to teach your dog that sharing is wonderful. Never punish a dog for guarding; that is a sure fire way to guarantee a bite down the road. Punishment only caps the beast; eventually it comes out and when it does it's not going to be good. So best to educate; shooting for a wagging tail instead of a tooth display.