What are people using to help their floor mats and area rugs from slipping on tile floors? I've got a small vinyl floor mat as a bathmat outside of my shower, and I'll be getting a matching runner to use in front of the vanity, but I'll need something underneath them to keep them from slipping. I've used plasticky grids that are supposed to be non-slip, but don't work. I see some others are a kind of spongy texture, like some shelf liners, but I don't know if they'd slide on tile floors. Or I've heard of spray products that you apply to the bottom of the mat or rug, that give it a non-slip texture.

Ideas?