I like the idea of this but having looked into the cost of the lead sheet it worked out quite costly; although it should last virtually forever. Maybe practical using scrap lead sheet/off cuts rather than brand new sheet.
Newspapers & Magazines in a large sized cereal box work fine, but messy to re-cycle pellets, so might try out old rags/clothes instead. Carpet layers as additional backstop is also good.
The rubber mulch in a box idea looks efficient, seen mention of this on bbs previously. Trouble is how big the sack of mulch would be.