Dogs dig for one of two reasons. The first reason dogs dig is out of boredom. The second reason is less common but does happen occasionally. Some dogs dig because they are scenting animals underground and want to dig them up. Assuming your problem falls into the boredom category where most do, this should help you. Very active dogs are the ones that dig and they need a lot of exercise. Give them a lot of attention and at least two long walks a day outside of his fenced in area, play games with him, and give him some training. If he is already adequately trained, do your own refresher course with him, including the “leave it” command for when you catch him in the act of digging.
Is your dog allowed in the house? Many dogs with excessive digging problems are outside only dogs. If your dog is sufficiently potty trained consider allowing it. If he is not adequately trained, check here for instructions to get started. It will decrease his boredom dramatically because he will be included in more family activities.
If that doesn’t solve the problem, you may want to consider making a place for him to dig and hiding weatherproof toys in there. This will give him something to do and save the rest of your yard. Think of a children’s sandbox possibly. He can actively search for toys and play with them once he has found them. You can even go out and play with him and the toys he’s found.
Try taking him places with you, giving him more attention, giving him more exercise, and working on obedience. This should help you to fix the problem. If it doesn’t, feel free to leave a comment for me and I’ll be happy to help as much as I can.