Yes Brian, I've noticed fishing lines are not thick enough (at least not my 40 lb variety). The squirrels have cut them on several occasions. I also tried aluminium wire, but it is too soft, as you say. Steel wire might do it, but it is very in flexible, and so not easy to throw over branches. Maybe a thin metal chain would do it, but I need the wire/chain too slide fairly frictionless over the branch, since I pull the feeders down and up when refilling seeds.