Stick a notice on your gate/fence/door saying 'to whoever complained please note it is NOT our dog that is barking'
or words to that effect.
If you are there with it, a water pistol is a good way of interrupting whatever it is they are barking at, but if you are not there you need to remove any triggers. I leave my curtains pulled on the french doors as they look through these and bark at the birds. I put a post box on the outside of the house as they will bark when the postman or anyone puts something through the letter box. I also put a rude note on the door saying visitors were not welcome without appointment (especially Jehovas Witnesses, Gas/Electric salespeople and other unidentified nutters. This has cut down the number of callers when I am not there. I had one neighbour who complained so much the council put in sound monitoring equipment, and they found out it was not my dogs at all, they were not barking for any length of time or at unsociable hours. I do agree though it puts you on edge and you tend to jump on them at the slightest bark.
Got good neighbours now, who are happy that our houses won't get broken in to!