I often think it would be a lot cheaper just to feed my dogs cat poop than to buy big bags of expensive food for them, they seem to like poop better anyway. The only solution I have found to this problem is to prevent access to the litter box. I have tried the boxes with doors on them and not only do they not keep the dogs out, if the dog sticks their face in there while the cat is doing their business the cat may never use that litter box again. Then you not only have the problem of dogs eating cat poop, you have a cat who will find a safer place in the house to go (usually your carpet).