We have battled fleas too, with our dogs anyway. They have a new medication for dogs called comfortis. It is a pill that you give your dogs once a month. It works wonders!!! Within a few hours you notice the fleas are less. You have to get it at the vets office. But so worth it!! I'm not sure what to do with them on chickens but at least it helps in the yard a little too when it's given to the dogs.
Comfortis has been out for several years now. We used to use it on our dogs until they had a nasty reaction from it!