dig around outside and put 18 inch heavy galvanized 1/4 inch screen nailed to posts with stainless nails. should have put rat fence in our buildings but never knew the problem it would be. Does help to put a return lip on wire. they dig down along wire and just hit more wire. 6 ich return works. Found that four foot high doubled over with lip works about the best. Same works with bin slabs. Lttle extra work and few bucks when building would have saved us a bunch over the years.. Once you do that the rats under the building will die anyway with no way out.