I have a pair of old body boading fins from quite a few years back (short stiff fins) that I would like to start using as an alternative fin when freediving occasional, for short powerful thrusts and giving me more manoverability. However (they are open healed) the fin straps at the back have either stretched or my feet have shrunk as now they are quite loose. Can anyone think of an easy way to shorten these rubber straps so that the fit is a lot tighter? And I'd rather not have to wear any socks to make up for the space. Any ideas are greatly appreciated! 
Thanks!
Martin
Thanks!
Martin