This is something that has already been practiced in the past. I heard that some drug cartels do it in Mexico still, but they're not so patient. It used to be done in China as punishment for treason or fratricide, for example. It was called 'death by a thousand cuts' or 'lingchi'. They would just tie up up the person and gradually cut off parts of flesh until the person died. I was going to share a link to read more about it, but the images are very graphic, so I'll let you Google it yourself. I still don't think this kind of punishment would stop rape. People aren't usually thinking very rationally when they rape somebody.