The only way to control rats is diligence and being uber-cleanly.
1. Keep all feed and food products swept up and secured in galvanized containers. Don't leave food out during the night and keep the storage area very clean.
2. Keep all piles cleaned up. Wood piles, brush piles, compost piles, refuse piles, clipping piles, etc. cleaned up and especially away from home and coop.
3. Build them out. Check your home and coop for small holes and sign for wear. An adult rat can fit through a hole the size of a quarter, so these are really easy to miss. If you see a series of holes in the ground, fill them in.
4. Clear away any tall brush and trees overhanging roofs. Rats are arboreal. They will use trees and tall bushes as pathways.
5. Any signs of urine or rat feces, clean up immediately. Rats use scent marking with their urine to leave messages for the colony (we rat fanciers call this Pee-mail). Use some 409 or other strong cleaner. Destroy the trails and it disrupts their ability to find their way.
6. Use snap traps. I discourage poison because the bodies tend to get places where humans don't want their bodies rotting.