Industrial floor/entrance mats (probably similar to the "Taco Bell" door mat mentioned earlier) work really well, the ones with the nice rubber bottom. Never slip or lose their ability to lay flat. Unfortunately they are kind of heavy and can be quite expensive to buy new. If you can find a place that is going out of business Im sure you could get one from them on the cheap. I found a lady at a flea market selling all kinds of sizes of these for pretty cheap. They were previously used but had been laundered. I bought one, good find. Ask around at flea markets, I think this might be like a thing that some people do.