I have used the Invisagrip, which works great, but for rulers that I infrequently use, I keep a can of old fashion Rubber Cement in the sewing room. A quick coating on the back is fantastic once it is dry and if it gets yucky looking with threads stuck to it, peels off easily leaving the ruler unharmed.
Never heard of the "Grippy Spray" - Might have to look into that!!