I was also thinking wolf, but we haven't actually seen a wolf in a burrow. We returned to take another look. The diameter of the entrance is ~18mm. It seems like the spider cut the nest cover to fit the hole, because it fit perfectly. The piece of paper wasp nest was visible under the stone, but wasn't covering the burrow entrance; it was up-ended and could have been blown by wind. I put it back over the hole and replaced the stone.