I live in the Pacific Northwest on a hill comprised of glacial till. Rocks up to the size of an ottoman are frequent. I have a plot about 75' by 75' I want to clear for a vegetable garden. It is currently a mix of elderberries, vine maple, sword ferns and balckberries. I want to remove the existing vegetation and larger rocks without destroying the soil, and then to rototill and ammend the soil. Anyone know what is the best power tool to get the vegetation and rocks out?