My guess would be squirrels looking for nuts. We've seen both in
our yard, especially in spring when the plants are new and the
nuts are few. Squirrels bury nuts all over then root them out
when they're hungry. Cats trying to get moles will do this,
too. I'd think a possum or raccoon would dig a larger/deeper
spot. What to do? I don't know. I'd think you could make a
million if you can figure it out.
Raleighgirl