Good idea, my shaft key on this boat is so long, it prohibits that from being done. Naturally, I could take it off and cut it in half, would still work fine. Not sure why that one was so long. It came with the shaft when I had a new one milled.
I like the inside idea (too) especially since any force is not probably really going to be all that heavy. Just looking for a little protection from an accidental 1" diameter hole in the boat someday

Rudder would most likely catch it.
Paul