Joby have a corded strap, specifically for DSLRs that is designed to automatically tighten around the wrist if the camera is dropped. Out of curiosity, I purchased one to try it out. It’s not expensive and does tighten around the wrist if the camera falls or drops out of your hand. It is very comfortable and I love the green color.
However, for you DIY hackers out there, you can fashion a similar wrist strap with a built-in wrist tightener from paracord using a slip-knot. Just do a google search to get a tutorial online.