We've been having trouble with rats too. We lost a 3 month old pullet to them in the otherwise secure coop one night a few weeks ago. We thought she was way too big to worry about rodents 
We put poison out in bait stations, but I found, our rats at least, are so dumb we have to witness where they're running at night and then put the stations directly in the path of their highway. Three horrible days of picking up dead stinky rat remains everywhere and being worried the chooks might find one before we did. But they didn't seem interested.
Now I think I have to move the stations again, still seeing some rats but they are hanging out in different spots.
We've also gotten more militant about cleaning up all feed and water sources. They will frequent your yard just for a drink, so we dump all outdoor waterers every night and check after rainstorms that nothing is collecting.
If the chookies spill any food we use the rake on it.
It's a pain in the behind but hopefully any survivors will take themselves back to the neighboring farm they came from.
We put poison out in bait stations, but I found, our rats at least, are so dumb we have to witness where they're running at night and then put the stations directly in the path of their highway. Three horrible days of picking up dead stinky rat remains everywhere and being worried the chooks might find one before we did. But they didn't seem interested.
Now I think I have to move the stations again, still seeing some rats but they are hanging out in different spots.
We've also gotten more militant about cleaning up all feed and water sources. They will frequent your yard just for a drink, so we dump all outdoor waterers every night and check after rainstorms that nothing is collecting.
If the chookies spill any food we use the rake on it.
It's a pain in the behind but hopefully any survivors will take themselves back to the neighboring farm they came from.
