My chicken pens are covered with old salvaged galvanized corrugated metal, like what barns are roofed with, and the stuff is full of nail holes. When it rains the water just goes right through those holes. Everything becomes a muddy mess. I was thinking maybe I could walk around underneath the roof (it's only 6' high), and squirt something from a tube to seal the holes. Maybe rubber cement? Something else? It's not an option to cover the roof with something else, so sealing the holes from underneath seems the best idea. But what would be the best substance to use?