Swallows in the Workshop

Have had a problem with Swallows in my shed ever since I built it. The little mongrels nest and infest it and of course everything gets covered in bird Poop Have counted up to 20 of them in there at one time Have tried shooting them with rat shot and they shoot through for a while but soon come back. Tried one of those plastic owls that BCF sell, they say the owls work well for keeping seagulls off boats. Obviously owls don't eat swallows 'cause the swallows didn't give a flying Proverbial about the plastic owl.
Then last week I found the remains of a weather balloon in my paddock. I thought I may as well try the reflector from that and lo and behold it worked a treat . I strung it up from the same line I had the Owl on at about 7.00pm and the swallows came in to roost just after it went up. Every one I saw come in perched for a couple of seconds, took a look at the reflector swinging in the Albany Doctor and shot through flat out. Here is a photo, it is about 600 mm across at the base made of that foil plastic cardboard stuff