if there is lots of rodents and shelter, feral cats can help with control better than anything else i would figure.
many years ago in New Zealand ,i worked for a pest destruction company.I remember the Maori foreman telling us about the way that he dealt with a problem of rats in a flour mill. Obviously it was not possible to use any kind of poison. his method:
1) cut the top out of a 44 gallon drum
2) caught 3 rats in live traps
3)put all three together in the drum
4) left them until there was only one rat ( rats and mice will turn cannibal under food and space pressures)
5) let the rat go ... once cannibal rats stay that way and will turn other rats
i have never had the situation to try this out, but have no reason to doubt the guy.