Fear comes in many forms. Fear is a common behavior issue in dogs and I have worked with many different fear based issues; all having different causes and levels. How you approach a solution to a fear based problem must be well thought out and researched. If you go head on; introducing the cause of fear at a 100% level; known as flooding, there is a great chance of more damage. I have a real soft spot for fearful dogs; its tough being in a human world without the benefit of speech.
If we are afraid of a situation, object or environment we can communicate our discomfort to the people around us. This lets everyone know upfront what is going on and why we may be acting in such a manner. For many dogs who are fearful; their guardian may not understand nor be able to help them tolerate or overcome their fear. Tackling fears should never be attempted with archaic methods of training or flooding. Force; both physical and mental only causes more fearful behaviors. Flooding is when someone puts the dog into their worst fear situation at a 100% level.
You must start working with a fear behavior at the lowest level of reaction; meaning you are looking for the point of reaction from the dog and want to move back from that. The best example I can explain this with is the very common arachnaphobia of humans, fear of spiders. The first step would probably be to drive by a building where there are known spiders, no spider in site. Getting closer to the building might take weeks or months depending on the level of your fear. But there is no point in trying to move to the next level; a more concentrated submergion if you cannot make it at the last level.
What you are trying to accomplish when working with a fear based behavior is to change the base behavior when around the fearful situation. Meaning that if your dog is unbelievably afraid of men wearing hats and has to this point barked, peed and basically come unglued; we want her to now look at men in hats as a good thing or at least non threatening. So you must take it slow; flooding puts your dog into a state of panic where nothing can be accomplished. You have to convince your dog that men in hats are a great thing and this is done with patience.
Slow and steady wins the race and definitely achieves a higher level of success when working with fear based behaviors. There is no hurry; each success should be a small one. I have broken some fear based behaviors down so small that no person other than the guardian and myself would even notice each step. A small success could be a glance; an ear raise or a change in body posture.
But wheatever your dogs fear; realized that this is very real to your dog. It is a sad way for a dog to live so do your research; hire a professional positive behavior specialist and help your dog to climb out of the fearful way of life they lead.