My Inlaws got this barking Muzzle thing after they recieved a letter about their dogs (It was only one of them) She is a boxer and would bark at anything.. Birds, cats, aeroplanes, fast moving clouds etc
They used to put it on her everytime she would start barking, she could still bark with it on but it was muffled and alot quieter.
They would leave it on for 10-15 mins then take it off.. After only about a week neighbours started complimenting them about how quiet bella had been.
Maybe you could put the dogs out as soon as you get up, or get up a little earlier every morning so that you have more time to monitor them.
As soon as she starts barking, put on the muzzle. After 10 - 15 mins of quiet time take it off. they just got theirs from a pet warehouse place so Im sure they are readily available!
Goodluck, barking dogs drive me bloody insane!!!