Keep on leash
Mine eats cat pooh, not dog pooh.
He really relishes it. And, once it's in his mouth and on his breath no one can tolerate being around him.
We keep our GSD on leash at all times he's not in the fenced yard or in the house or in his pen. Too many cars around not to.
When he tried to ear pooh or even when he licks the grass where, apparently, another dog has pissed I give him a strong correction. Over time, he doesn't even go near poop anymore.
Why don't you just keep yours on leash?