Deal with a neighbor's barking dog by making the neighbor aware of the situation, asking him to resolve the problem, and then following up with the proper authorities if the problem isn't resolved. Landlords, property managers and the police are all resources to use if the problem can't be resolved amicably between the neighbors.
Document the days and times the barking occurred, as well as the duration of the barking, to have on hand in case the complaint has to be escalated to the authorities. Attempt to resolve the situation amicably first. A neighbor might not be aware that his dog barks excessively when he is at work, and once notified of the situation, he may be able to resolve the problem quickly. If he is aware of the barking, he might not realize the neighbors are affected by the noise. If the relationship is already friendly, call or visit briefly to ask him to quiet the dog.
If no relationship exists, leaving a note is a good first step that avoids direct conflict. Mention the dates and times of the barking, as well as the impact it has on the other neighbors. Suggest resources to help with training, such as websites or local dog trainers. Do not make threats, and thank the neighbor in advance for his attention to the problem.
Wait a few days to contact the neighbor again. He may report back that he's working on training the dog, in which case patience is necessary. If the barking has not improved, and he is unresponsive after the second request, report the problem to the authorities. Depending on local laws, landlords, property managers, homeowner associations and the police may all be good resources for help.