Another suggestion would be a GOOD obedience class. A basic obedience class should teach a good, solid stay. Even though you are still near, it teaches the dog he can be apart from you and still be safe. The dog must stay in the same place/postion you put him in, while you walk away, and eventually return. The distance will gradually increase, the length of time the dog is required to stay increases, and distractions will be added. The advanced obedience classes include out of sight stays, where the dog is required to remain sitting or in the down position for a specific length of time with the handler out of sight. You would never leave a dog on a stay when you leave the house for any reason other than training, but the training itself can give the dog confidence. Just another thought!