The target like SRTA uses is great! I also made one several years ago when I had an archery range here at my home. It lasted for 2-3 years with several people shooting it 365 days per year.
But for a backstop, carpet, old rugs, floormats, or industrial mining belt will do well. Whichever you decide to use, only hang it by the top, allowing the bottom to swing. That way it'll absorb more energy. Especially the mining belt. That stuff is tuff to remove a point from, and if you make it unmoveable, you'll stick a bunch of them.
hnh