You can probably pick up an old but serviceable Gravely walkbehind with the 30' bushhog deck for a few $hundred on ebay. Anything that I can fit under that deck on mine is annihilated and it's very manueverable. It uses a bushog-weight blade (about 3/8 thick), so it can deal with a few rocks (concrete blocks, old barbed wire, dead cats, etc.) I'm kinda surprised that I've never seen a flail attachment for the old Gravelys. I'm in the process now of rebuilding a 60" sickle for mine. Sickles are also available in 42" for pretty cheap.