Our adopted St. Bernard mix hides food in the strangest places...?

We adopted Duke on mothers day of last year. He was 7 years old at the time and no one knew where he had come from or his history. No matter how much food he has, even if we make sure he has food in his bowel 24 hours a day, he will hide snacks and food EVERYWHERE. We had given him a ham bone and he stuffed it between the cushions on our love seat (which only he sits on) he has hidden his doggy treats in my son's laundry basket, he stole pizza crusts from the garbage and hid them under my daughters dresser and no matter what time of day, if you pick up his blanket on our bedroom floor, it will have 2 cups of dry food hidden in the folds. He carries them in his mouth, clear across the house to bury them in his blanket. I don't mind this at all, It doesn't upset me in the least, but I do want him to know that he doesn't NEED to do this. How do I help him.