bungie cables are springy, and have alot of "give"
May I suggest pneumatic tubing?
My team is using pneumatic tubing (2 strands of it at varying heights) to keep balls out from under our robot.
It has alot less "give" and pushes the balls straight back out with no problem...
It is also slightly stretchy, so even putting it about 4 inches off the floor (like we have on our robot) it can still negotiate the bump with no friction to hold it back, and they spring right back into place.
Use a "G" sized drill bit to drill through what you want to mount it to, then use a #10 bolt (about a 3/4 inch length) and a nice washer to keep it from going back through the hole...
the #10 bolts work beautifully on pneumatic tubing, and form an almost indestructible bond when threaded all the way into the tube...
this is just my $0.02 suggestion
we were testing the "impenetrability" of the undercarriage of our robot, and one of the members threw the ball at the side of the bot, and the tubing threw it straight back at him with ehough force to knock the glasses right off his face lol
and it did not even break the 3" plane rule
