Not sure about lines or string, but I know the black plastic poultry netting can last for years (e.g. more than a decade), and if supported by a post (with a proper diameter topping) it can/will also withstand heavy snowfall. Most snow passes through, but enough can stick that a small diameter support post can end up being pushed through the top. ....doesn't take much to cheaply increase the diameter of the support as we ended up using the lid from 1 gallon ice cream pails (which was enough to spread the weight of the mesh/snow at my parents place in MN).