ah I went with the sisal as I'm fairly averse to using plastics, especially outdoors, whenever it can be reasonably avoided (once a year I remove a literal truck load of trash from along my frontage, mostly plastic). sisal is supposed to be plenty strong and sunlight resistant, but whenever it breaks I'll just repair it. plus as I grow the hedge I can abandon the string without concern. haven't decided what kind of plants yet tho - still need to do my homework. I already have some wild berry bushes in the area of the fence that are pretty thorny, so that's a start.