I use "Invisi-Grip". It comes in a small roll/sheet (maybe 12 x 24 or something, don't have a new package right now to check), you can cut the size you need, peel off the backing and place it on your rulers. It's clear and is a static-cling kind of product, so you can move it. I have it on the backs of all my rulers. When you apply pressure, it doesn't slip while you're cutting. On the smaller rulers, I cover the whole back. On larger ones, just use several strips. I learned about this in my very first quilting class and I'm hooked.