Help for non-slip rubber rug pads

I use those rubber pads under rugs to keep them from sliding around, especially in the bathroom. I find that they work great when I first put them down, but after I pull them up one time, they don't stick to the floor again. Is there a trick to getting them to stick again? It seems a shame to have to get new ones every time you have to scrub the floor, but mine are useless after I break that seal for the first time.