Tyr's issue with eating inappropriate items went deeper than just training an "out". It was a subtle rebellion against my desire to put some rules into playing with balls/tugs. He'd be all over his ball until I asked for him to bring it back to me. Then he'd lose all interest in his toy and go off to find other things to play with - broken glass, aluminum cans, etc.
When I finally realized his loss of interest in the toy wasn't a drive issue but was a "screw you and your rules, I'll go find my own toys" issue, I laid down new rules - You either play with my toy and follow my rules or you don't play at all - he quit with the dangerous stuff and was thrilled to play fetch.