You got the right sub, congrats! He is from Germany.

As for what happened in the session, you're sooo close! Although there was no bungee cord used for that purpose, at least not the way you're thinking here. I did use a few bungee cords, but for other purposes. If you look closely at the red bungee cords, you might be able to figure out what they're being used for. (Hint: they are there to prevent him from being able to do something quick and easy...that would make his predicament much easier after that point.) 

As for the green and yellow bungee cords, you may not be able to figure those out until you see the full pics. The positioning of these bungees were designed to prevent a bit of cheating, something he was trying to do to make the predicament easier to endure for longer, but I used bungees here to make it a gradual effect rather than a hard stop type of thing (and if anything, this part may have prevented something in the area of injury, although I don't see that ever happening here anyway). 

As for preventing injury in general, I didn't have anything in this predicament that would put him at any reasonable risk for injury. Between the fact that things would pull off/unattach pretty quickly, and this sub is pretty smart and follows my work very closely to have some idea how I set him up in this one even if he couldn't see it, I was confident that he would know what to do if things went in that direction, to prevent anything like that from happening. Would it hurt? Yes. Would he feel it the next day? Likely. Plenty of incentive to not take the easy way out. But no injury. ;-)