I didn't have any rubber lying around this time. I thought a wooden foot would be nice, a peg leg for a laptop! I decided to make them out of paper though.
I sewed a throwing sling earlier this week. It's fun to use. With the right rocks, it works well.
Edit: A noose is not so good for the end that stays attached to your finger. It tightens when you throw bigger rocks, and is uncomfortable. Best to just tie a single loop knot, and adjust it so it fits like you want.