IMBED TARGET INTO THE BACK STOP AND THROW A SHOVEL OF DIRT IN BACK AND ALONG SIDES THEN YOU DO NOT NEED TO WORRY ABOUT RUN AWAYS. I THINK THAT WOULD BOTHER ME MORE ABOUT HITTING CHAIN AND NOT KNOWING WHERE IT WENT. MAYBE IT WILL HIT YOUR EAR MUFFS THEN YOU'LD KNOW WHERE IT WENT.USING A CHAIN IS ALWAYS DANGEROUS ROUND ANYTHING IS AN ACCIDENT WAITTING TO HAPPEN. SHOOT ANY TYPE OF ROUND OVER 3500 + AND YOU HAD BETTER KNOW WHERE IT IS AT ALL TIMES, HECK EVEN A 22L HAS BEEN KNOWN TO HIT A ROCK OR WATER AND TRAVEL WELL OVER A HALF A MILE TUMBLING....
You want alloy chain...
I heard that using old firehouse or steel wire works well. I've also heard of people using leather straps which can take a few more shots and are easy to replace. Or, you can just take a piece of angle iron and weld the plate to it and have a fixed swinging target and be done with it.
Para-cord may be another option- good for a lot of weight, strong and much smaller diameter so less chance of getting hit. in the event it does, very easy and quick to repair.