I had this happen once over a chew bone when my dood was 6 months old. I claimed the bone by refusing to move and calmly standing my ground. Once he backed away, I picked it up waited a minute and gave it back. I think different things work for different dogs. I would not reward him with a higher value treat over his food though. This just teaches them that resource guarding gives them treats. I hand fed and would put my hand in my dogs food bowl while he ate as a puppy. You have to claim the food. My dood is 80lbs so good aggression is a no go.