The best de rocking machine I've even seen was one we made out of Caterpillar 613 scraper When I worked at the cat house, We added long root teeth to the cutting edge and teeth to the elevator chain constructed a slim large diameter trammel behind the elevator chain left the rolling floor slightly back from under the trammel to allow the dirt to fall back to the ground the machine would drive through a plowed field pick up rocks and deposit them in the bowl when the bowl was full the elevator and chain raised the floor slid back then the ejector door would push them out.