We had a bit of a rat problem not long ago, they were attacking the feed bins and picking up the spilt feed.
We invested in some profesional trap's, we found them on e-bay and they were highly effective. We caught 4 Adult rats in a week then we left an open feed bin out with a little feed in the bottom, and caught the young. Never had a problem after that.
Your proberly wondering what we did with the young... piece of 4x2 timber job done!
Personaly i wouldnt use poison, it's not worth the risk of it getting eaten by one of your own animals or some other poor wildlife. Trapping in my eyes is also far more humane, quick and clean, poison on the other hand is a long drawn out no doubt painful death, nothing deserves that.
BB