Here are a few pics of things I've done. All were used where they had a chance to pop some rocks up. None reliably brought any rocks up larger than a softball.
The first drag I built was for the
B7500, and the original setup was simply a pair of chains to drag it. The adjustment for how aggressive it became was by selecting form the choices of holes for the chain attachment in the leading flange of the first I-beam. Angular adjustment was shortening one or the other chain. When it became apparent it would be nice to pick it up for transport, it was a simple matter to us the lift boom.
The latest version with the original I-beams uses a big old blind flange. The flange adds weight and makes it easy to adjust the angle by dropping a pin through different bolt holes. Aggressiveness is via top link adjustment.
The big one was sketched up by me and built by some guys in our shop. Three sides are I-beams we had laying around and the front has sections of pipe added to keep the ends of the I-beams from digging in.