In Dragonball Z, when Gohan changed into an Ozoro, Piccolo found an appropriate solution, destroy the moon. Easy-peasy.

The real question is, when Goku used his Genki Dama (on two occasions, by the way), it never resulted in anything more than a relatively small crater. With all the power stored inside that sphere (easy above a billion, and over 9000), shouldn't it have caused a bit more damage? Piccolo managed to destroy the moon, easily, with power level of less than 1000.