Paracord works if that's what you have, but for cheap, I prefer setline, made for fishing. Or, presumably mason's line works well too. If I'm going to spend the money on something more optimal, I'd go with some form of UHMWPE (i.e. Spectra or Dyneema). It's lighter, thinner, stronger, and doesn't hold water. It does have the disadvantage that it's extremely slippery and doesn't hold a knot. There are however, versions with a non-slip coating made specifically for guy lines. I know the bushcraft crowd likes paracord though, because it can be deconstructed and the strands used separately.