Fill the hole almost all the way. About a inch from the top lay some chicken wire fencing down, and then finish filling it. When the dogs tries to dig and drags it nails across the wire it will stop. Worked like a charm for my dog.
dogs dig generally out of boredom. maybe you need to spend more time with him, take him to a dog park or more frequent walks, or he needs someone to play with? not suggesting you get another dog, just doggy playdates or more outings with you.
Dogs get destructive when you leave them alone to long. It's how a lot of dogs act when they have separation anxiety. Spend more time with your dog and maybe keep him close to you more so he doesn't feel like a loner.