One of the "runners" at one of our local clubs is similar to the ones described. It carries a couple pulleys so that it can slide down the slightly downhill cable. A rope is attached to the end of the 3D target and that rope routes along until it meets it's "spool", this is a tire rim with a handle where you simply wind up the target to reset it. They drilled a hole in the side of the rim to insert a stop pin so anyone can release it by simply pulling it out. It's a pretty smooth system that is alot of fun.