Dont worry about the planes .. they will come of far worse if they find your lines, the people flying them know that and should keep well away.
They too are supposed to keep to a section of the Downs, they have their own rules and restrictions on a notice at the top near the car park.
Last time I want to the Downs I fancied a go at my Super 10. Could I launch it alone ?? no,, and I could almost feel the other kiters giggling ..... none offered to help. Baaaaa-humbug.