Concrete all around the edge of the building so nothing can dig in. The bottom also has 5" of compacted limestone nearly as solid as concrete, 6" of sand, and a 2" thick stall mat. Solid steel frame stalls with 2x4's going 5' up then 2x2" metal bars an inch apart another 4-5'. I covered the bars in hardware cloth(mesh wire) and the top with poultry netting to keep out any birds of prey. At night the doors are locked shut and nothing can even get in the building. I've come across nothing but a cat that can jump up the side of a stall and they can't get over the bars. Rats and various vermin have gotten trapped in the stalls cause they can't jump or climb out.