You could try the dried potato route. I did this last spring when the rats started showing up. They can't get in the coops at night, so we put out pile after pile of dried potatoes. Took a little time, but we started finding bloated, dead rats laying about here and there. It also seemed to make them easier to catch for the kitties. Plus, we've got owls that do more than their fair share.
I haven't had good luck with poison, but I also haven't tried many out. I may have to give the brand
@cmom recommends to see if that takes their numbers down a bit.