I have used my Bush-Hog branded tiller(10 acres) for eight years.I has taken a beating in my rock infested fields.
May sure you use a slip clutch and its working.I leave my discharge flap wide open and for the most part it just spits the rocks out the back.Once in a while it will pick up a flat stone and jam,thats what the clutch is for.I have picked "tons" of rock and still they pop up.I have miles of stone fences,the farm is 150 years old.