I have a large, self healing mat from my grandmother that's quite old (yet it still looks new). I also have a square blue one I bought from Wal-Mart. The older one is thick, like the 54" ones from Joann's, and the blue one from Wal-Mart is the thin kind that needs to be replaced every so often. They both slide, so I was wondering what I could use to keep them in place.