we made a back stop on our shooting range a few years ago. we just took the rototiller, went up to the top of the shooting range, and started digging. we took the loose dirt, and piled it in back of the "shooting pit". this pit makes a nice place to rest targets, and it is safe. we took the top 6 inches off in the back, and the top inch or so off in the front. we also dug up the neighbor guys field, and picked some more up. overall, our back stop was about 5 feet high, and about 3 feet thick. that will stop a slug any day.