We can't concretely identify the source of the hole-digging as many animals (especially those foraging at night) can dig into lawns and gardens looking for insects, even if those insects are not numerous enough to be causing plant problems. Skunks, raccoons, squirrels, and chipmunks are among the usual suspects, especially in late summer and early autumn. Iowa State's flowchart of diagnosing holes in the yard might narrow-down some possibilities, though it's not an exhaustive list.

The stump appears to not be chewed but rather pecked, possibly by a Pileated Woodpecker or another woodpecker looking for insects that are eating the decaying wood. Pileated Woodpeckers are large birds (about crow-sized) and as such commonly chip off sizeable chunks of wood with their pecking; they've also been observed foraging like this very close to the ground, which most other woodpeckers tend not to do. It's also possible this is a skunk or another small mammal prying off the outer wood layers looking for the same food source -- wood-boring insects.

Miri