Invisgrip works great. It really helped me a lot. I now use it on the back of all of my rulers. I also got one of those suction cup handles to put on my ruler which also seemed to improve things a lot. Are you "walking your hand " up the length of the ruler as you cut? That, too, seemed to help me a lot. I had exactly the same problem you are having. Believer me, all of a sudden one day you will have just practiced often enough and it will happen. In the meantime, cut slowly!!