Omnigrid puts out several sizes of Ruler grips. The one I use on my 24x6 inch ruler has a suction cup at each end. You can buy them at Joanns or go to Harbor Freight and for half the price they have a similar item that they use as a safety handle in the bath tub area. Ended my ruler slipping because your weight is evenly distributed on the whole ruler surface.

Maybe I shouldn't tell you but I paid .50 at a yard sale for one. ( still in the wrapper not used )

The first time I saw one was last summer, I told my husband about it . He went down in the basement and came up with two. It was a little longer and red and black. He said these are to carry sheets of glass. It seems they came in pkgs of two.

Put a few flat dabs of hot glue on the back of your rulers or cut some little pieces from the waffly shelf liner that many put under their foot controls. Either will work to keep the ruler from slipping.

Fantastic idea