My Mattie, 11 weeks old, is also a poop eater
While at the Vets 2 weeks ago I asked them about this. He said that this is a Terrior trade and that hopefully they out grow it. The best advise he gave me was to scold him when he was caught in the act. So we have been leaving his poop on the wee wee pads for just a few minutes afterward to see what he does. If he goes for it we yell at him and tell him NO NO..... and that has been helping. Good luck.