Blue blocks of poison bait spiked to the walls in many of the outbuildings on the farm seem to keep me rat free. Plus a few barn cats. I had good luck with the old Victor rat and gopher traps with peanut butter on the bait pan. Have not seen a rat in a few years now. The local pest control officer makes his rounds once in a while to check most farms and can supply the bait. Of course is has to be in buildings or boxes that dogs and cats can't get at. 
Its also entertaining to watch the guys with night vision scopes and pellet rifles picking them off in the dark. 
https://youtu.be/WaO8zmIAvn0?si=dQn9CBMbafe3vmg2#mce_temp_url#