Our local range that I' ve been going to for years does that exact thing (indoor range). They' ve got 5 lanes in front of 5' x5' ' blocks' of compressed-stacked cardboard (they' ve got blocks on top with screw vises through them to keep everything in place). They get it from local businesses, it' s only like 18" thick, but it' ll stop an arrow in a big ol' hurry, even when I' m shooting 125#.

Only problem is that broadheads rip them up bad, so they aren' t allowed there. (I shoot expandable C.O.I' s, so I don' t have to worry about it though.)