Back when I cared about my yard, I used something similar to above post. The dogs had a large sandbox filled with dirt and sand. They could dig to their hearts' content in there. To teach them to do so and keep them interested, I would hide treats, toys ect in the dirt for them to find.

Now that I have more dogs, I've given up hope and just try to remember where the "human traps" are!

You might try burying his feces in the holes when you fill them. That stops some dogs.