Do you have a photo of the area where you saw the damage? Were there any tracks or feces in the area that could be used to help narrow list of possible culprits? Do you have a "no dig" skirt in place around your coop/run? Is your coop open or does it have a solid floor that would be an additional barrier to anything that did manage to burrow under it?
I don't have a picture right now, but I will try to get one. I didn't see any tracks or anything. My coop is secure where the nesting boxes and roosting bars are, and the chickens aren't in their run at night. We put some sticks in front of the holes that were dug so if anything else we will be able to tell.