Ok, here's what I did, and it worked. I buried a blown up balloon. Coco (God rest her soul) was an evil digger. She would dig holes all over the yard - I had more twisted ankles after we got her, that I lost track. One day, I got an idea to blow up a balloon, very carefully put it in the major hole that she was currently working on and very carefully covered it with dirt. I let her out and stepped away from the door and watched her from the window.
I kid you not, this dog looked back and forth at the window and the side yard about 10 times, then headed for that stunning dirt pile...
Furious digging, then "POP!!!"
...she must have gone 10 feet backwards in midair. I laughed so hard I though I was going to pass out.
Never dug again.
Beth