I usually buy hanks of mountain climbing rope out at Smith and Edwards in their Rope room. Most of what they sell in their odds and ends bin are 50' in length and work well for high lines. But I do have to tighten them almost daily.
If I'm around the trailer, I usually use a nylon strap with a ratchet to tighten them up. But packed in, I usually don't bring the excess weight along and have to retighten my truckers knot each day.