Followup 1.5 years later - mice soon ate every bar or chunk of Irish Spring that I put under the house. No deterrent effect at all.
The camera down there shows a critter parade under the house nearly every night. Another camera on the deck, same. Everybody trotting the length of the house then a while later coming back in the opposite direction.
Skunk, raccoons, foxes are the most common, possum and bobcat occasionally. And deer occasionally sampling the houseplants on the deck in the middle of the night, waking us up.