I live in suburbia, so even if I wanted to shoot said hawk (I don't, for reasons I'll get to in a minute), I couldn't......not to mention jepordizing my CCW, hunting privileges, ect.
I don't think a few pigeons in my yard would be considered "stock" by any judge,
anywhere, and said hawk does provide a service by taking care of the squirrels and woodchucks that have decimated my garden in the past.
There is a top on the coop, so that idea won't work....checking out the pigeon fanciers websites is a good idea, however.
I was thinking about maybe stretching some chicken wire above the coop and hooking it up to a small battery to shock anything landing on it......not enough to cause death, but discourage it hanging around the pen. Then again, if my 'homers' try to land on it, they might get discouraged and fly elsewhere as well!