Answer: Under an oak tree? Probably squirrels. There's not much you can do to deter them - they are looking for treasures under the mulch and even if you raked every last acorn out of the soil, they would still be inclined to explore the area just to see if you missed any. You might try laying a chicken wire barrier so they can't dig. Sometimes deterrents work but once the squirrels get used to the smell, they are no longer afraid. Changing or alternating deterrents might work. Try Deer Away and alternate with Critter Ridder. Wish I had more suggestions!
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