TRY THIS
Get yourself some garden gloves and some treats, go to an area in the yard where it's okay for him to dig (must be somewhere the poor guy can do what comes naturally for him)
Then start digging like a dog in that spot. Reward him when he starts digging, and bury treats in the new spot. Continue to bury treats in the new hole daily and whenever you see him digging there say "GOOD BOY DIG" Then you'll be able to say "GO DIG" and soon he'll just go to his spot. When it gets to big fill it in with shovel and let him dig it up again. You can spray a variety of nasty "no dig" products into his current holes or fill them with rocks to further discourage digging in none dig zone area.
GOOD LUCK!!