Summarize the following:
You want to set the stage for a nice talk about the dog without him getting defensive. The best way to do this is to make initial contact at a time that he doesn’t feel caught off guard. Make sure you phrase this first interaction as finding a time you can both talk. Then, if he is happy to talk about it right then and there, you may be able to settle the issue in one day.  You might try going over on a Saturday morning when you hear him using lawn tools. Don’t enter his property until invited, and try not to sneak up or surprise him. Break the ice with some small talk about how his week went, and then ask them if he has time to talk about the dog soon. If your neighbor gets angrily defensive or violent and threatens you in this talk or any future talk, stop trying to solve the problem yourself. Go to the police and tell them about the barking, and that a simple, polite request prompted your neighbor to threaten you. They may be uninformed about the problem, either not aware of the barking or not knowledgeable about what to do about it.  A friendly heads-up, along with some tactful mentions of dog care strategies, perhaps even noting a dog trainer you've heard produces good results, may be all it takes. The neighbor may not be aware that the dog is causing a problem, for instance if the dog barks while he is away at work. After initial contact, or a planned conversation, your neighbors may feel regret and want to address the problem immediately. Allowing them to handle the problem themselves help you will keep your relationship civil. They may have tactics for handling their dogs barking that they haven’t had enough time to do lately. Give your neighbor time to make changes.  It can take time to adjust schedules and/or conduct training sessions that will help curb barking. It is entirely possible that your neighbor is either reluctant (doesn’t care enough to act) or recalcitrant (takes offense at the mere suggestion of doing something), which may require further action on your part.  But remain cordial as much as possible. Having conversations in daylight and in public, such as during Saturday morning yard work, can help you keep the interaction safe and out in the open. There are many ways to prevent barking, including daily exercise and training sessions. Learn about several possible options and mention them to your neighbor in a polite manner. Try to treat the process as a negotiation of conditions that you both can accept.  This will help you in the eyes of the law if things do devolve into an intractable dispute. If the neighbor is open to the idea, and you are willing to take on the cost/effort, you can even offer to pay for an anti-bark collar, or help them find a skilled dog trainer.  You are under no obligation to do this, of course. You may find that this is often much easier than befriending the human neighbor.  Learn the dog's name from the owner, and ask to be introduced. If the dog gets to know you, it may be less likely to bark at you. The next time it barks, try saying its name in a reassuring voice. With the owner's permission, give the dog a toy or treat to show you're friendly, and to calm it down.  If you can build up some level of friendly rapport with both neighbor and dog, you may even choose to offer to walk the dog during the day — for instance, if the dog barks each afternoon while the owner is at work.  Getting involved in this way is always your choice, however.  If you don’t like dogs, don’t have one because you don’t want the responsibilities of caring for one, or are plenty busy caring for your own dog, you absolutely don’t have to offer to help with your neighbor’s yappy mutt. If your neighbor ignores you, contact him one more time. Let him know you have asked the barking a few times, but it is not improving. You want this to remain a dialogue between the two of you, but you will get neighbors involved if necessary. At this stage, you probably don’t want to threaten contacting the police yet, unless they are acting violent or threatening you. Continue to gather evidence while you wait. Give your neighbor time to find a solution, but prepare for the next step in case this doesn't work. Maintain a detailed journal of how often the dog barks and for how long, or talk to other neighbors who have been as annoyed as you. If the neighbor seems unwilling to make an effort, this can come in handy moving forward.

Summary:
Find a good time to visit your neighbor. Presume that your neighbor is unaware. Let your neighbors address the problem. Make second contact. Suggest anti-barking strategies. Befriend the dog. Issue a final complaint. Keep track of the continuing problem.