i used a large dog crate to bring my goose home in. but i have used boxes when someone was coming to get ducklings. I cut out holes for breathing on both side not large enough to get their heads out of, then once inside the box i use shipping tape to close up the top. If they are inside a fence he can probably herd them slowly into a corner or a building pick up with wings held close to their body and hand closed around neck to keep bill away from face.