I made a W whip using cord in the method illustrated at www.tothewoods.net on a new 138" long 1.6 oz ripstop hammock. It slipped and I fell 12 inches. No harm done. Before, I have used the zip tie on both a 10' and 11' hammock with no channel and no mishap yet. Only one thing differed in the new hammock: I didn't hem the ends. This morning, I sewed a rolled hem to one end and applied a zip tie to both ends. The unhemmed end slipped. Then I hemmed the remaining end and retested, but instead of passively sitting and lying in the hammock, I hopped in, bouncing up and down vigorously (with two Thermarest mattresses on the ground below). Both ends held. For me, the rolled hem I used on the ends of the first two hammocks prevented slippage.
The zip ties hold. Not sure I should "fix" it by undoing and running the zip through a tunnel.
I usually do well learning from pictures, reading and videos, but I completely failed at whipping ripstop.