Originally Posted by ChrisH
While I don't disagree with you, I use the self tensioning line that you speak of (HC4U's second one in his thread) and they also turn a stake into a projectile.
There are several ways of doing them - the two most common, one shock cord based and one slingshot rubber based, both have a "maximum stretch" set by the fact that the stretchy material is run parallel to a normal guyline. That means that only a certain amount of energy can be stored in the elasticity of the material, and also means that things won't go flying if the stretchy part snaps. It's much safer than a standard bungee, which can stretch much further, store more elastic energy, and send stakes flying at a higher velocity.