Stall mats. They're heavy carbonized rubber, around 3/4" thick.  We use them in our platform kennels to cut down on drafts, protect the wood, and make a more comfortable surface for the dogs. Around $40 for a 4x6 heavy stall mat. They also come in 2x4 size.  Do not get the ones with a pattern on one side. Flat smooth surfaces are easier to clean. Dogs CAN gnaw off a corner, but it takes a very long time and a lot of determination. These won't tear up quickly. I like the larger ones because there are fewer seams when you put them down, but the smaller ones are easier to handle.