For a safer target try plywood without a stiff backing. Hang it by ropes, if a piece is large enough then set the support low and the plywood will bend and absorb a lot of impact, reducing bounce from the knife. Plywood won't last long though.
Welcome to the Yard! Great people and great knives here - hope you stay around and chat with us! I don't really have enough room to be hanging plywood in my apartment (and I'd hate to miss and stab one of my kids!!!), but I'll remember that for when I get a big enough place!
Anyways, welcome to the Scrapyard community, better known as THE YARD!!
