You are all trying to correct bad behavior, which is what it looks like to you. To the dog, it's his basic instinct, and you can't beat it, shame it or train it out of him. It's like teaching a dog not to eat, it can't be done. It only confuses him.
The dog is following his instinct, which is to burrow. Canines are pack animals and used to nesting in dens. You have to give the it a place to build its den and he/she will leave the rest of the ground alone.
Next to the house where there's afternoon shade, build a flat wood platform roughly 3' x 3' (depends on how big the dog is), six inches to a foot off the ground. Make sure it has a back and sides, with only one way in and out. It should be sized so he can get in and turn around, but low enough that he can't stand up in it. If you slant it down in the back, even better. They like to feel the top of the den at their back. (Ever sit with your own back to the wall in a restaurant? Same idea). He'll dig under the platform and leave the rest of the yard alone. He's only trying to find shade and protection from his natural enemies.