I have a 120 year old home in the Puget Sound region that was built with a post and pier foundation with 18-30″ clearance. A foundation (aka skirting or perimeter walls) without a footing were later added. It is well ventilated with one vent being an 8′ tight screened barrier. As it is waterfront, the supply of rats seems infinite. This mostly dry space is about 912 sq.ft. including a small low budget cellar. The cellar does have a sump pump. Currently, I have fiberglass bats and a vapor barrier. The rats have loved it for decades. I am trying to figure out a long term solution to my rats. I’ve plugged holes, but it is likely that they have burrowed under the foundation walls. There is no food there for them. Poison doesn’t stop them. A sonic device must be like music to their ears. I’ve heard good and bad about 2″ of closed cell foam. I’ve heard good and bad about a rat slab. I’ve heard about rigid foam insulation around the foundation walls. I’ve experienced very limited suggestions from various sales people. They do seem to agree that I have a problem that won’t go away, due to the concrete block foundation without a footing that allows the rats to burrow. What is a long term advisable solution to getting my rats to pack their bags and move out of “rat haven”?