My latest great find is 3M non skid tape for bathtubs and showers. Get the clear coarse grit stuff. Amazon has it. Cut little pieces about a quarter inch wide and a half inch long (or a bit smaller) and stick one piece in each corner, on the underside of your cutting rulers. If it's a long ruler you can put a piece in the center of the long sides, near the edge. Your rulers will absolutely, positively not slip, guaranteed! You can't even slide the ruler a smidgen. It has to be picked up and repositioned.