Just toggle your slippery half-hitch. I've been doing that for years. Find a toggle (a little bit of branch, etc.), tie your slippery half-hitch, place the toggle through the slippery loop, then pull the tail down snug on the toggle. When you are ready to untie, you can pull the toggle out, or just break it (it's a branch and you aren't taking it with you).
"One of the best things you can do in this world is take a nap in the woods." ~ Jayber Crow by Wendell Berry
"While it may be a lot of work, the view is best from the summit." ~ an anonymous staff member of Philmont Scout Ranch
Enjoy the day