As well as the treat, you have to keep on saying "Good Boy". Also, when you get the treasure off him, give him a treat, say Good Boy and give the treasure back to him (sounds crazy, but stay with me here, OK
) I recently had this with Nelly, my son bought bones for both the dogs when he was home a couple of weeks ago. Dillon was fine, but Nelly was snarling & growling. I offered Nelly a treat & kept on saying "Good Girl". Eventually, she dropped the bone and ate the treat. I repeated the sequence for about an hour & a half to convince her that she could give her treasure to me without risk. Some treasures have to be kept by you (socks, knickers, dangerous items etc) but others (toys etc) can be given back to the dog. While he's learning though, always give back the treasure a few times, so that he knows he can let you have it & you will give it back. Just practise regularly with things that he's holding, offer a treat, say "Good Boy give" or something, then give the treat when he's given. They learn very quickly.