I don't know about you, but I like the sandpaper circles that you can put on the underside of an OmniGrid rotary cutting ruler. You know, the yellow and black ones. There is a drawback to these sandpaper circles, though. They are big and hard to see through.
Yes, I've tried that clear vinyl that clings by static. My ruler still slipped.
Here's my solution:
a package of self-adhesive 220 grit fine sandpaper
a .25" hole punch
a .125" hole punch
a pair of tweezers
The .25" hole punch cuts out a circle the exact size of the circled markings on the ruler. The .125" hole punch cuts out a circle the size needed to go down the diagonal of the square rulers. If you peel off the backing off the sandpaper dot and stick it on the backside of the ruler right at the yellow dot of the ruler (the tweezers are really handy at this point) the sandpaper cannot be seen from the right side of the ruler.