I have a liriope border that's running wild. On the front side, it's held in check by grass. On the back side, it's spreading hither and yon. I like the lirope and I want to keep it, but I'd like to contain it with some sort of edging from materials on hand. Not really interested in wood, although getting some pallets and pounding in slats might be ok. I'd really like to have something that doesn't disintegrate. Heard of using discarded rain gutter material but I don't have any. What about cutting up plastic milk bottles into strips and pounding those in? Too flexible?