Where I live, the ground grows rocks, everything from 8inch to 2inch. I'm not kidding, I can mow one week, clear out all the rocks and by the next week another crop has grown. I have the entire yard tilled up right now, I would like to go about a 6 inches down and at least for one season not chuck any stones through another window.
Maybe take a standard one and weld some 1 inch expanded metal on it or something.