I used a rather unconventional approach at times when I feel flies are multipling faster than I can keep up with....
I go let the girls out of coop to free range
I poop scoope the poop board and any other poop I can find into sand castle building play sand bucket and add just a bit of moisture (water) to wet it down a bit to make it irresistable to the flies but not dripping wet nor a toilet bowl!
I then unroll one of those flypaper traps that are long and sticky and carefully place it in the bucket above the wet poop. I then place bucket on coop roof or other locations near by that the girls won;t get into it. Several times throughout the day I will rearrange the fly paper to expose areas of it that does not have flies attached already. Also, rewet poop if it has dried out too much.
I usually catch no less than one hundred to 200 flys this way in just a single day on a single flytrap. It is litterally (sp sic ?) covered almost solidly on both sides with flys, and so much so that when handled, by the ends of course, it feels like it would "fly away" if you would let go of it and it is buzzing like crazy!
I also use sweet PDZ and DE as needed in and around the coop, which eliminates other attractive "spots" for flys! Which makes my trap even more attractive! I think it is the combination of these actions that makes it work so well.
Good Luck,