Some cats just do this, there isn't anything that will stop them. We had one that would pee on anything fabric left on the floor - bath rugs, throw rugs, clothes, towels, anything. Thankfully we didn't have wall to wall carpet. The boxes were clean, she used them so it wasn't a litter issues. There was just something about the texture I guess that made her do it. Like previous posters have said, either get rid of the rugs all together or hang them up when not in use.