Actually, you might have much better efficiency with a cake or bar poison than D-con. Rodents tend to pocket the D-Con in their cheeks and store it for eating later...which means they can transport it from your "safe" place to a place your chickens may eventually be exposed. It also means the rodents may not eat it right away, thus having time to breed more replacements before dying.
The bar or cake poisons consist of large blocks of poison that must be gnawed upon in order to get any off it....meaning they ingest it right then and they don't carry pellets that look all the world like pelleted chicken feed into your coops. To a chicken, a pellet is a pellet. The rodents also can't carry the blocks to another location for later eating...unless they are enormously large rats, which are a whole 'nother problem.