I hate to be negative, but the one thing I don't like about methods like this is that you're grinding the line around the tree when you tighten it, and on fragile bark I've seen it sawing into the surface. I prefer to tie the line in a loop around the tree, then use that to tighten up the tarp, so you aren't moving the line relative to the tree.
Here's a picture of what I'm talking about, using a figure 9 to tighten it. My tarp line has a loop in the end - I wrap that line around the tree then feed it back through the loop. Once it's put in place, it doesn't move around relative to the tree when you're tightening your tarp. The line is fixed to the tree and you just tighten it up to the tarp ring, using your trucker's hitch or figure 9 or whatever.