So we spent several hours setting that up. There is a tremendous knowledge of the rope, knots, and how this was going to play out. I wouldn't recommend most people trying to set that up, but the rope was anchored incredibly well. It also was doubled over, and attached both at the back of the harness by the neck, and the front of the harness in case anything went wrong. The rope we used has 11% stretch to it, however, after it got wet the first time we figured that it would be less springy. That is the reason for the person standing at the bottom, to pull Mike if it didn't snap and just drug him along the water.
For the means of length, I couldn't include the whole set-up process, but it was incredibly well thought out and planned, and it worked perfectly how it was envisioned. Good response and concerns tho!