That's such a disgusting habit! Chihuahuas seem to be the worst for eating poop, and I have three of them.
There are several types of pills available that are supposed to make poop taste bad. I know, you would think that it already tastes bad, but apparently not to a dog. The ones that contain capstan seem to work the best, and my dogs really like the pills. They think they are treats.
If your dogs are getting their "snacks" from the cat's litter box this won't work because cats hate the pills. I've found that getting a covered litter box with a little flap for a door solves the problem. Even though my little chihuahuas can get in easily they don't seem to want to.