I have sandpaper dots on one ruler- plastic dots on one - invisagrip on another. They all work great. You have to use a full length and width of invisagrip on the bottom of the ruler, pieces won't work. Be generous with the dots - sandpaper or plastic. You have to walk your fingers up the ruler while cutting long strips. A simple way to not cut your fingers is to keep them away from the ruler edge. Learning how to cut with a rotary cutter takes practice.