Looks like a whiplash knot on reverse twisted fiber. The right hand piece goes over the double cord above the last twist forming a bight  then go around behind and then up through the bight. Do it again and tighten

I tried a couple versions of what I thought you might mean walter and I must be still doing something wrong.

I also think the issue is where to pull the tie off fibers from. ie which part of the twist is best to section off 10 or 15 fibers to be the tie off at the end of the twist. I'll just keep trying. 

Blowgunman that knot in the video works great when you are ending a sling with a 5 braid but not so well with a rope twist ending.

Tomas it's an epic struggle that only God, and apparently Luis Pons Livermore can answer.

Don't you find that it slides a quarter to half inch after 30-50  throws? No matter how tight I make it, it still does this to me. 

Thanks guys.

I think I finally have it figured out. I had about 25-30 fiber sisal strands to make the knot. This was too many! I reduced it to 5 strands and again used the knot that Luis showed in the video and it worked. It was just too thick as my hand brushed against the whip upon release. It would slowly pull on the 25 strands, making it slip. 

Thanks!

EDIT:  _________________________________

Okay it does still slip but only that 1/4 inch that I mentioned before. It holds its place after the 1/4 inch slip so I just tie the knot 1/4 inch higher than it should be, then it will slip into place.