i had two pitbulls that used to eat out of my cats litterbox when they were puppies, they eventually grew out of it.
Luckily so far Lefty's been scared of poop. after he poops he stares at it, then sniffs it and looks at me like "wow, did that just come out of ME?!?
EWWW THAT STINKS, PICK IT UP ALREADY GIRLY" then he runs away from it. he hasn't raided the kitty litter for my cats poop yet *thank god*.
they have a name for poop-eating, it's called . . .
Coprophagia
here's a link about it . . .
http://www.vetinfo.com/dencyclopedia/decoprophagia.html