Floating rope I'll let Addy answer, But other options are flexible tubing, PVC circle, or a foam center for a wreath available at places like Hobby lobby, although this are kind of big and bulky they do work well and the green ones blend in with the plants. I have used them in a actual fishing pond with great success in keeping some for the pond but not allowing them to take it over. simply, your wanting to make a floating circle or shape to keep the plants bunched together. Flexible tubing is easy, a two to four foot piece of tubing, I prefer black over clear as the black won't show algae growth on it as bad and it blends in well, but either will work, take and place one end of the tubing in hot boiling water for about two minutes, this will make that end very soft and flexible, insert the other end (cool end) of the tubing into the end that that is hot and push it into it as far as possible. once that is done run it under cool water, the hot end will seal around the cool end and may the tubing hold air inside and it floats. be sure to get all the water out of the tubing before putting them together. you can also do the same thing with PVC tubing, a straight piece of pipe a 45 a straight piece of pipe a 45 so on and so forth until they come and make a complete circle. the shorter the straight pieces the smaller the ring. Put them all together, BTW they don't have to be glued to work, but gluing them once your sure on size will help stop water from leaking in over a longer period of time when being used when the temp's start changing, going from hot to cold and back to hot allows the pipe to swell and contract and some water may get in over time. Hope this helps.
