I changed out our rain barrel filter today and shot this quick video to show how we keep leaves and roof debris from entering our barrels.
Simply wrap a nylon stocking over the funnel between your downspout or diverter and your barrel. Insert the closed end of the stocking into the barrel and let it hang down. Debris will collect at the end, but won’t impede the flow of water (at least not for a while), since the stocking stretches and remains permeable above the debris.