If you give them enough to climb on in the cage it won't really matter so much if they can't climb the plastic. If you do use something on the sides of the cage just make sure not to use any sort of tape to attach it or anything that the geckos could get stuck or caught up in. Also be careful of using rocks--I know some people do with no problems, but my concern is that the gecko might jump or fall and a rock is a really hard thing to land on.