How can I stop my dogs from eating from my cat litter pans?

I scoop my cats litter pans daily but my dogs still get into them for the feces "treats". Is there anything I can do to prevent this? My dogs are very determined and 'fooling them" by turning the pans' opening toward the wall as the vet suggested just isn't working. My dogs are large enough to pull the pans out away from the wall or turn them around.