I used a the tractor supply subsoiler to dig out the foundation for my house. I've got a 55 hp tractor. At 4 feet I hit a sandstone ledge that would come off in layers if I could get a corner to get the subsoiler under it. It was long slow work. I finally got to the point where I couldn't do any more, and I hired a backhoe. Many times my wheels would spin when the subsoiler got a grip under the rock, but couldn't get it up. I didn't kill it very often. The backhoe got down a little further. I was convinced by this experience that the backhoe could have done in one day what I spent 10 days doing with my tractor, fel, and subsoiler.