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It is natural and normal for dogs to guard high value food, toys, or areas they perceive are being threatened by other people or dogs. This behavior is so natural that we address is not through expectations that we can stop this behavior, but by teaching a strongly enforced drop it / leave it command.
“Leave it” is taught using items or food your dog finds low value. Using these low stakes items/treats, your dog is taught that they will be rewarded for moving away from the object or will be told “no” if they move towards the object. “No” is used as a word that marks what is unacceptable and is followed by a negative consequence.
Once your dog demonstrates that they understand what “leave it” means, they will move on to practicing the command with higher and higher value items and treats.
This allows dogs to play/eat what they love most, but clearly communicates that they must step away when told so their humans can safely reclaim the item.