Sometimes, dogs exhibit a behavior called resource guarding: they become aggressive toward people (or other dogs) who get too close to something the dog values quite highly. It doesn't necessarily have to be food either - some dogs can get very attached to their toys, or blankets or even a grubby old stick they found in the garden.

Resource guarding is one of those behaviors that is better prevented early in their life rather than having to be cured later in life once the habit is well established. So if you get a dog as a puppy, start working right away to prevent him from guarding his food dish. Teach him that any time you reach for it, something wonderful is going to happen.

For instance, suppose you normally feed your puppy kibble. From time to time, walk up to your puppy while he's eating and drop a piece of something wonderful in his dish, like a piece of hot dog, roast chicken, or liver, or a dab of canned tuna.

This shows your puppy that when your hands come near his dish, it's not because you're going to take his food away. It's because you're going to give him something even better. If you have other people in your family, have them play this same game with your puppy.

If you adopt an older dog, you can try the same technique, but proceed with caution. If you observe any signs of aggression (such as growling, baring teeth, snapping, nipping, or biting) you should consult a behaviorist or experienced trainer to put together a behavior modification program that will keep you safe.

Bonus tip: Trade up toys, too.

Practice showing your dog that when you take toys away, it means good things, also. Give your dog a toy she doesn't care about as much. Take it from her, then immediately hand her a favorite toy.