Slidelock rulers are one of the best purchases I ever made:
https://www.quiltersslidelock.com/slidelock-models/
I use the Slidelocks both to cut with, and just to place on top of other rulers before cutting. They help enormously with slippage and keep my ruler hand high and out of the way of the cutter.
If you can't afford the Slidelocks, the best ruler grips I tried (and I tried about half a dozen different types) are the grip strips:
https://www.amazon.com/Guidelines4qu...dp/B009DF9DLA/
I have even used them under one of my June Tailor Shape Cut mats.
You do not need grip strips if you get Slidelocks.