Dogs eat poo for many reasons, Merlin started it when he was on antibiotics for a long time, Bonnie and Tilly eat it because Merlin did.
I tried everything on the market I could find, nothing worked, the poo eating still went on, now I don't have Merlin it is a lot less, the only poo that is eaten is Ellie's.
I found I was really stressed and was stressing Merlin, it is normal for a dog, it isn't for us, I gave up on this, the stress went and we all relaxed.