Just something to consider. I had wind surfing straps on my boat for some time. They can be adjusted to be pretty loose, if you're worried about ankle damage. Plus they have the benifit of some support when standing on top of them (helps when chop hits your foot, but you don't want to be all the way back in the strap).
They are a bit more expensive than the rope method, but an old second hand pair may be cheap?
Chau
Clint