Or...

You can do what I did for my niece.  I had a few sausages that I was cutting with a very large sharp knife while I was talking to him about how well he should treat my niece. And how stupid young boys were with trying to get the girls to have sex with them or force themselves on the girls.

The visual was enough for him.  His eyes were REALLY wide as he watched me slice sausage and talk to him about the responsibility of keeping his dick in his pants.