I have used those clear "buttons" that you put on the bottom of things to protect the surface, on the ruler too. You can also find them at the dollar store. Then I found this clear sheet (at Joann's) to put on the back of the ruler, it just clings on. It works well, but recently it starts to peel at a corner of one of the rulers, I think it's from me trying to shove it in the crowded place.