I have rulers that are slip-proof for cutting fabric and I love them (Olfa brand is my favourite).
I also need to cut squares of paper and paper backed fusible web for my Give & Take Applique workshops. This is often more difficult than cutting fabric since all the rulers I have tried slide on the paper. It is important that I give students accurately cut paper and fusible web for the workshop exercises.
I decided to try Grip Strips™ by Guidelines 4 Quilting (www.guidelines4quilting.com). These are 1/4" wide clear plastic strips with a sticky back.
I followed the instructions and put them on the underside of my ruler, near the edges. I found that they 'lock' my ruler in place while cutting. I have tried other products to make my rulers 'unslippable' and they make it more difficult to slide the ruler into position. The Grip Strips didn't do that. My ruler could slide easily as I positioned it and when I held it in place the pressure was concentrated along the edges where the Grip Strips are.
These worked like magic! No more slipping and it makes this job fast, easy and accurate! If you have trouble with your ruler slipping - even on fabric - give these a try.