If you want the bottom of the floating plant ring to be protected from nibbling fish, here is a link to the floating plant holders that I have bought and used every year since 1997 to start my floaters in in the spring. Once they grow enough, I let them free (by then the fish lose interest).
http://aqua-mart.com/show.pl?cmd=showsubcats&subcatid=135If the bottom doesn't have to be netted, then you can just cut an old piece of garden hose, seal the ends together, tie a small rope to it, and attach it to the side of the pond. Mine holds water hyacinth in the spring but now, I use it as the only hyacinth-free zone to feed the fish (like a big feeding ring).