Lenox look into what is called a weed razor. It is like a rake except it has a blade on each side and a rope tied to the handle. You throw it out and yank it back in and it cuts the weeds off at the bottom you can then pull the weeds out. You might try to find an energetic teenager( I know it's hard to find one that is willing to work hard) . On a pond that size you could keep quite a bit of it under control.
