If you have bait and traps down and you are still bothered by rats then they must still be getting at a food source namely what you feed to your Hens and Ducks, can the rats get in to your hen house to get at any feed and do you keep your feed in metal bins with a good secure lid to make it rat proof, if you feed liberally by throwing food about outside this could be why the rats do not bother with the bait, if you do feed in this way make sure that all is cleared up by your poultry and ducks before you leave, if you still have problems have a go at smoking them out by using the gases from a chainsaw or some small petrol engine by attaching a tube to fit down the rat holes, actually this is good fun watching them bolt and trying to crack them when they bolt, :)