I also second cats. I have a lot of friends that have barn cats to rid the rat population.
You often can find feral cats in rescue services around your area.
I chose not to because of the baby chicks, a house cat, and of course my rat terrior.
But if you can get a couple of rescue feral barn...
Comrade, I feel your pain. I too am in a waged war with rats. I don't know if you've ever seen Ratatouille, but I am an eyelash distance from becoming that crazed old woman in the introductory scene that shot gun blasts her ceiling to kill the darn things as they swarm out of the house. I HATE...