The auto parts factory I worked in had propane fired cannons, but they were to scare off the birds, not protect from hail. The birds would get used to them, so they had to rotate through recorded startle calls and pneumatic whistles every few weeks. We had a couple of power sub-stations at the plant, and the birds loved them for some reason. The scaring was not entirely successful, and we had a few transformer blowouts due to fried birds.