This is a non-stop issue with ranges. There will always be ricochets. The single best thing a range can do is build smart. I find regular people seem to think you can push up a mound of dirt 10 feet high or shoot into woods and hve that be a bullet trap.
What you need is a good range design. Good methodology is something like:
-30 foot mound of dirt at the maximum range
-~10 foot mounds at each sub range distance with fixed target boards
-elevated firing position
-range bed of sand, pea gravel, mulch or other relatively bullet absorbing material
-strict enforcement of muzzle on the back stop or below rules
-trees on the back stop or leaving tall natural trees behind it for catching stray ricochets
These are ideas for flat landers. Building against a mountain is also a good idea.