To prevent resource guarding, your dog should be taught the Leave It command. This command is used to tell your dog that she may earn something even better from you for leaving something she might be tempted to steal and/or guard.
To teach the Leave It, begin with a piece of kibble or other relatively boring edible item. Arm yourself with a bowl or treat pouch full of more highly-valued food items, such as tiny pieces of hot dog or chicken.
Sit down on the floor with your dog and place the boring food item (the “forbidden” item) on the floor in front of you. As you do so, say “Leave It” in a firm but kind voice and cover the item with your hand. If your dog tries to nose or paw at your hand to get at the food item, hold your hand tight over the item until she quits trying. One second after she quits trying and instead pulls her head away from your hand, praise happily and deliver a treat from your pouch and simultaneously pick up the forbidden food.
Read the entire article at http://www.petbehaviorchange.com/blog/2017/12/13/how-to-teach-leave-it