My two yo cocker will still eat nasties of every kind. I give him probiotics and yoghurt, try to walk him not hungry but he's still a dustbin. At the moment goose-poo is his passion. I have tried Leave it! training but success is patchy. I'm coming to terms with never really being able to control what he eats. I just watch him like a hawk and only intervene if it is plastic or other non-digestables. I don't think of muzzling him because he wouldn't enjoy walks so much. If you do use a muzzle just make sure it's the biggest box-muzzle that's tolerated.( And make sure you stop and remove it and offer drinks in heat.) But it really bothers me and I've no solution.