Dancing rulers!
 

Finally, I solved the dilemma of my long ruler dancing across my fabric while trying to cut long strips. I had purchased and was using the Invisigrip by Omnigrid...not impressed. Years ago my father-in-law gave me some sandpaper that is sticky on the back. Works like a dream. The only problem is that you can't see thru it, so I just cut it into small squares and place it randomly on the ruler. I don't know what it cost, but it is probably cheaper than the Invisigrip I had purchased.

The only problem I am having now is that it grips too good...no more sliding the ruler around on the fabric. I have to pick it up and place it where I want it, but guess what? I have true straight cuts.

that's why I use this https://www.walmart.com/ip/Curad-Tea...-0-CT/51179938
it's out of stock online, but i buy it at my local store. i am very, very happy with it.

This is what I am using. The one roll should last me a lifetime. I also put several layers of it on my machine bed to help with the 1/4" seam.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

They make a skateboard grip that is clear and works well.

I have this tape on some rulers other things on other rulers. Cheap and it works great.

That's what HandiGrip is, a clear sandpaper with sticky on the back. It really works great!

This is what I use and I love it

The online Jordan Fabrics tutorials show using a hand weight on the end of a long ruler to keep it from shifting as you work along the ruler. Seems like a great idea.

I have clear sticky rubber 'feet' - probably about 1/4" thick that I stick on the 4 corners of my rulers. Works wonders. No slipping at all. Got them originally (I think) at my sewing machine dealer but have seen them elsewhere (JoAnns??) as well.

It's worked for me
 

I was at a retreat and someone asked to use my ruler. She said do you care if I fix it? She pulls out this tape and puts it on my ruler and now I know why she is such an accurate and amazing quilter. She told me you can buy it at any local pharmacy and she was right.