I had a foster dog that would eat her poop, the other dogs poop, or dirt that looked like poop. She just didn't care. We solved this within a month (we only had her a month) by not letting her outside unless we were with her and every time she went to sniff a poop, we said "Leave it". If she didn't, we would walk over to her and take her by the scruff of the neck and say "Leave it" again. She learned quickly!
I don't think putting something in the dogs food is a good idea because they aren't learning that the behavior is incorrect. It doesn't take very long of "babysitting" them to teach them that it is incorrect.
The plus side is that her new owners reported she is excellent with the "Leave it" command with other things. We didn't tell them why she is so good at it. :)
