Is there a way to keep armadillos from digging up my yard?

Yes. Kill them. Did you know that barbecued armadillo is really good to eat. It's a very pretty white meat. You could electrify your yard for night time activity, like installing an electric fence, with the low wire about six inches from the ground. They will keep returning as long as they find something to eat, like grub worms, insects, etc., so you would have to eliminate their food supply. When I see a dead one by the road, I say "that's a good armadillo". Armadillos are a nuisance.