I like the Invisi-grip and use it on all of my rulers. I tried the sandpaper dots, but I don't care for them.
http://www.joann.com/omnigrid-invisi...x36-/prd17402/
Also, when you are cutting, do not put all of your fingers on the ruler. Keep the last 2 on the table and the rest on the ruler. It really does help keep it from moving.