 that he has his own scent already out there in the backyard may be exactly what you need to get him to go. So I would take some of his poop, even dab up some of his urine if he's doing it, and just put it around the backyard, go out there, wait it out with him. Once he goes out there once or twice, your problem's over and done with. Now, the important thing is to make sure you clean up the inside of the house properly. Make sure you've cleaned up all areas where the dog has gone with a good stain and odor remover made specifically for pets.