We've liked using cotton mason's line to outline the borders of the beds in the garden, because it's nice white and visible, and it doesn't stretch. Unfortunately, after a few months in the weather, it just comes apart, and we've been spending a lot of time replacing it. I think next year we'll be using sisal binder twine or something else that will last the whole season. We can still use the mason's line for row markers, which don't have to last more than a few weeks. Garden and learn!