I have Invisigrip on my rulers too and still get some slippage. Could be that I've lost a lot of strength in my hands. Dr tested last week and was surprised that the left is much stronger than the right (good thing I can write with both).
but i've started trying just a small piece of painters tape where it won't obstruct my view & its not bad. We're all different & not 1 thing works for everybody.
i tried the sandpaper dots but they kept coming off