Most use trained ferrets. It turns out, that in nature, one of the favorite targets of weasels, minks, ferrets, stoats, etc. are furry rodents like rats and mice. One of nature's most potent forms of rodent control. They seek them out and will go on killing sprees. Which offers one additional...
As for the what and how to of using bait blocks...........I asked a professional pest exterminator what he used and it was this........
https://www.belllabs.com/bell-labs/product/us/pest-control/contrac-all-weather-blox
And would be served up from this...
This the thread you are looking for.....
https://www.backyardchickens.com/threads/rats-when-the-army-went-to-war-on-them.1216226/page-2
......which also links to a thread which reviews a rat proof feeder. The latter is what will enable you to feed your birds, yet not feed the rats. Starving...