Haven't read all the replies, so don't know if this suggestion was added. Forgive the redundancy if it has. I have used the sand paper dots, the gripper and a couple of other things. The best advice I ever received, and the only thing that has worked for me is to use my hand. Yes, that's right. Put your hand flat onto the ruler. Then move your pinkie, your ring finger, and part of the palm of your hand off the ruler and on to the cutting board. If you remember to do this, you will have no more problems with your ruler slipping.