Of all canine behavior problems, fearfulness, in its many forms, is the most common. Fearfulness accounts for a considerable proportion of dog aggression, separation anxiety, storm phobia, noise phobia (a canine version of post traumatic stress disorder) and social anxiety. Because these conditions can be difficult to turn around, the preferred strategy is to prevent them from developing in the first place. That's why I want to spread the word far and wide about the critical importance of the so-called "sensitive" period of learning, when a dog is between 3 and 12 weeks old. There may be a secondary, slightly less sensitive period of fairly rapid learning that lasts till a dog about six months of age but, after that, what you see is what you get.
Trainers who tell you to bring your fearful two-year-old fearful dog to a dog park to “socialize” him are actually using the term incorrectly. It is possible to desensitize a dog to other dogs—so a fearful dog might accept a few other dogs into his inner sanctum of trust—but the time for real socialization has passed. In one study we conducted at Tufts, dogs that exhibited fear-based aggression toward people or other dogs were more than 500 times more likely to have been raised in less-than-optimal conditions with inadequate exposure to other dogs or people.
This means that an essential part of raising a pup is to spend that sensitive period socializing him and getting him accustomed to people and events to which he'll be exposed later in life. Proper socialization of very young pups to people and other dogs should be organized and orchestrated, not just left to happenstance. Ensure your pup's needs are met and that they're not left alone for extended periods. This enhances their confidence and will help prevent separation anxiety or what we call "submissive urination." Also, it's possible that exposure to low volumes of certain sounds, including storm sounds, during the sensitive period of learning may help prevent noise phobia and storm phobia.
The bottom line: Proper attention during the relatively short period of early puppyhood can help prevent a good deal of misery down the road, for both dogs and their owners.