Betty loves to dig too. I don't let her have the run of the yard. If I did she would probably be a walking dirtball!
I walk her on a retractable leash in the yard. That way, I can keep her away from the 'bad areas'. Sometimes, I will take the leash off for a few minutes in an enclosed area for some exercise...but I am right there with her. Or, if I am working outside, I put her on a long leash and attach her to a stake NEAR ME so she can run around a little without getting into too much trouble!