I agree with everyone else. The only thing (next to death) that is foolproof in the wizarding world is an Unbreakable Vow. Dumbledore couldn't said, with any degree of certainty, that he knew Snape would never betray him without that in place. I think it was the only means to keep Snape in line. He was always in it for himself and only cared abour Lily's preservation, not Harry's. I think more was at risk by not having him enter into a Vow. |