If your hills are anything like ours (foothills of the Cumberland Plateau) de-rocking is about as practical as emptying the ocean with a bucket brigade. Every good rain and EVERY freeze-thaw cycle our hills present us with a whole new crop of stone wall components. I pick up the bug ones by hand, the middle size ones are the toughest, but the landscape rake with every other tooth removed does a fair job. The amsll ones aren't worth the trouble. Most of ours are lime or sandstone and often pretty soft so they do break down. Every once in a while we'll get a chunk of something really hard and solid.
VistanTN