This is not my idea. It is from message #2505 of the HammockCamping Yahoo! Group. This small addition is worth the 30-40 minutes it takes to install them. It costs all of $5, a bit of spit (I didn't use soap) and a pair of needle-nose plyers. Here are a couple of pics.
My comments in red.
A Wrist Rocket uses two pieces of rubber surgical tubing about 6 inches long separated by a leather pouch. The two free ends fit over the aluminum frame of the slingshot which is form fit to go over your wrist for support and then up through your fist. Surgical tubing is very stretchy and tough (as in not breaking).
Go to Wal-Mart and buy a set of replacement tubes and pouch for a sling-shot. It costs all of $4.
So, what I've done (courtesy of Jerry Goller who taught me this in the first place...which is why I call it the Goller Grabber) is cut off the tubing where it attaches to the pouch (Jerry "undoes" the loop that it makes but I find it's easier to cut it and make a new loop around the ring on the fly).
I cut off the pouch instead of cutting the tubes. This allows you to see what the final "loop" will look like and it means you can skip the next step since a hole will already be along the one end. Just undo the loop and continue.
I take a nail or other pointy skewering tool and poke a hole in one wall of the tubing about a half-inch from one end (the whole goes through only one side of the tubing...not both).
Remove the line that is attached to the ring on the fly tie-out.
Then I feed the one end of the tubing through the plastic ring the fly cord was attached to until the ring is just below the hole I just skewered through.
Then I reach through the opening on the short end of the tube (near the skewered hole) with a pair of needle nose pliers, out through the little skewer hole and grab the long end of the tube (which puts the plastic ring under the pliers). Then I pull the long end of the tubing through the little hole and out the top of the tube. (A bit of spit on the tube helps it slide through the hole easier.) This traps the ring in the tubing and when I've gotten the tubing pulled all the way through it ends up rolled over itself just like when it's attached to the leather pouch. It will never let go of the ring this way. The only way to get it off is cut it or break the ring. (Picture #1)
Now I take a 1/4" nylon spacer (Home Depot/Lowes -- 25 cents each or so) and run the old fly cord up through the center (a nylon spacer is a hard plastic cylinder with a hole running the length -- the 1/4" dia one is about an inch or so long and has a hole running down the length about 3/32" or so in dia---big enough for the cord). I tie the cord with a couple of knots. Then for insurance I superglue the knot. (I just melted the knot a bit with a bic lighter.) The knot has to keep the cord from being able to be pulled back out the spacer but not much larger than the diameter of the spacer or you can't get the spacer in the tubing.
Next step is to put a little dish soap (I used spit) on the spacer and push it into the open end of the tubing until the spacer is all the way into the tubing and the rubber closes in around the cord that extends out the spacer (about 1/8"). The soap (spit) makes it easier. Or if it gets difficult I'll use the needlenose pliers to grab the leading edge of the tubing and pull it over the spacer. (Picture #2)
Repeat procedure on the other fly tie-out.
All done, there's a 5 inch rubber tube with the fly ring captured in something like a larkshead running to the cord which is held captive in the nylon spacer.
When setting up the fly I tie it out so the rubber tubing is pretty extended (stretched). Then as the fabric loosens up or rain stretches the fabric, the rubber tubing contracts on itself and tightens the fly...it becomes self-tensioning.
This works regardless of the type of hammock you're using. It just happens I have a Hennessey.