I cut round steel rod of various diameters into 1/4" thick discs, drill a hole close to the edge and thread thin wire through to make hooks. I have them hanging from trees. There is no backstop to these if I miss, but I live on a farm and there is nothing for miles behind them so it's safe to shoot. I also found some heavy gauge [4" square] reinforcing 'mesh' and hang a number of discs [also some old spoons] in each square. By cutting off the bottom [horizontal] length of steel I can simply push the 'legs' into the ground and it stands freely. I re-spray them every so often with livestock marker in a bright colour that makes it easy to see each hit through a scope. These discs, when hit dead-centre, give off a very satisfying sound. Another metal target I use is the domed part of domestic taps - they ring like a bell when hit if hung on a string. However pellets will ricochet of the rounded surface in any direction so be careful about where and when you might use such targets unless you hang them in an enclosed 'target box' or have acres of 'empty' space as do I.
Jim
Via Ballarat
Australia