I wonder how they do with covering them back up.
I watched my sister's 7 month old border collie baby do just that last week!.
We were talking in her dining room, which has a sliding glass door into the backyard. As we talked, he started digging, but since it's a new house and has no grass, it didn't matter. He dug all the way down so he was about half in the hole, just the top of his head visible. Then he got up, turned around, and dug all the dirt he'd just taken OUT of the hole back INTO the hole, then continued down to his ears again. Dug the dirt back into THIS hole. Then, standing at an angle, proceeded to dig a hole where he'd been standing BETWEEN the first to holes. I was baffled. When I asked my sister what the h*ll he was doing she just laughed and said, "Just watch him."
He proceeded to dig dirt out of holes and into holes in about a 4 square foot area pretty methodically for almost 2 hours, non stop. (I think he must be part badger, not pure border collie, incidentally. And not just because of the digging.)
THEN, after all the holes in this excavation of his were surprisingly evenly dug and filled in, he dragged his outside tarp over the top of the whole area, flopped down on it and went to sleep. His sister the shepherd mix joined him.
Now I know why my sister hasn't sodded or planted grass in her yard. She's waiting for her dog to rototill it for her, the lazyass girl.