I always prefer lazy farms! The observers are constantly on guard for melons to grow!
and when a melon grows the observer uses their piston attachments to kill the pumpkin and melons!
the dead melons and pumpkins fall into the water to be carried into pit of lava to be destroyed!
You will never see such a efficient melon killing set up!
edit2: I got to thank maggiadaskan(sp?) for help building the farm!