I like esshup's hog panel modification.
I don't think I would attach two cables to the panel. If it gets caught on something, you might pull it apart. I would just use one cable, and attach the panel to the cable. Eight attachment points might be better than two.
I also might avoid designing the "perfect" system. If you attempt to get ALL of the algae in a single pass, then you are going to catch a lot of organisms that you want to keep in the pond. I don't think you need the panel to hang perfectly vertical. If you drag it slowly it should grab a lot of algae even if it runs through at an angle.
If you get a significant portion of the algae on the bank and in a position where the decay nutrients DO NOT run back into the pond, then you have won a major victory against future algae growth by getting those nutrients out of the pond.
