OTF
Coney Island Whitefish Biologist
Keep a 20" piece of paracord somewhere and you should be able to fashion up enough of a strap to keep the fin secure in an emergency.
Straying off topic, but this is good advice and I'm surprised so few people seem to carry a general purpose piece of cordage with them underwater. It's great for jury rigging all sorts of stuff without having to cut up your spool, or sometimes you need something stronger than cave line. I've used mine for jury rigging broken mask/fin straps, jury rigging slings to lift stuff with my SMB, makeshift jon line, camera and light lanyard, tying gear to the tag line, securing gear on the boat, tying extra weights or whatever to the flag spool among other things.