Cheryl Phillips of Phillips Fiber Art used a piece of packaging tape, make a circle with the adhesive on the outside, place under the ruler and you are done. I have gone to her website and she now sells little gripper circles for her rulers. a more permanent solution. You wanted a idea right now, so this does work.

The quickest and easiest is to spray the back lightly with a spray adhesive and let it dry it lasts a long time and can be easily removed with nail polish remover

Nail polish/salt
 

I have tried this on three of my most used rulers and it works great. I put several spots on each ruler, perhaps 8 on the back of my 6x28. We use sea salt and the grind is course. For a few days there was a few grains which had worked loose, but okay now. Give it a try. I think you will be pleased.

Thanks for this tip.

Those are good size dots of polish. Will your ruler still lay flat?

I am going to give it a try. thanks

I tried the nail polish trick and found out the salt wears off and has to be reapplied.

I will keep this in mind but my favorite is the flat clear plastic circles you put on glass to keep from scratching surfaces. I have used them for years and never had one fall off. I buy them in the hardware store, sometimes the $1 store has them too.

Best thing I have found so rulers won't slip is Nexcare flexible clear tape. You find it in the first aid section at the store. It works wonderful. Hope you will try it.

Have you ever tried using rubber cement on the back side of your ruler? It does not deface or scar the ruler and will roll up when you are through. It does not slip on the fabric.