The only success I had with this was just making sure the dogs couldn't get to the litter box. Make sure the litter box is the enclosed style, with just an opening for the cat to get it. What I did was put the litter box under a desk, with the opening facing the wall. Only leave just enough room for the cat to squeeze through (assuming your dog is bigger than your cat). You might need to put a weight of some sort on top of the box too, depending on how strong/determined your dog is.