Part of the hotwire that I'm running down to the pasture from the charger at our house goes through parts of the holler in which there are no good trees to nail insulators on. I talked about this project here. I can't hammer a post or a piece of rebar in the ground to attach an insulator either because much of the sloping hillside is limestone bedrock and outcroppings. So I started making the insulators like the ones above.
It's just some plastic tubing and baling wire off of a straw bale tied in a loop. That is, I had some hollow plastic tubing which I pushed some wire into. I twisted this into a loop around the hot wire. Then I attatched another piece of wire around a tree and through the loop. The tension on the line keeps the hotwire in place. I can use smaller, scraggly trees as posts this way, and there's no shortage of those downslope. It costs me like 5 cents an insulator this way, if that.