Dog attacks. This may not seem like much of a concern, but the statistics point the other way. Every year, thousands of people are the victims of a dog attack. Most such attacks happen in otherwise peaceful suburban neighborhoods. A dog might be a man's best friend, domesticated for thousands of years, but that doesn't mean that it isn't an animal capable of being a vicious natural predator.
You perhaps know a dog who is badly behaved and bullies everyone in the neighborhood. As a child, I knew one such dog who terrorized all the kids in the neighborhood and made it impossible to head outside the home without adult company. Anybody who has been the victim of a dog attack, or has even lived under the shadow of a prospective attack knows how terrifying an ordeal it can be.
So how does one prevent a dog attack?
The best way, of course, is prevention. Simply avoid the areas where you know a badly behaved dog is bound to be. Dogs are territorial animals and will defend their turf, particularly if they find you threatening. Avoidance is the best way to prevent an attack.
The kind of clothing you wear can also make you susceptible to attack. Dogs like to look people in the eyes and are generally suspicious of those that have their head covered. If you are wearing baggy, loose clothing, you may attract a dog's attention too.
There are certain tools/weapons you can use to scare away a dog in case of an attack. One of these tools is a dog chaser whistle. This whistle produces a high frequency sound (above 20,000 Hz - the hearing range of human beings) that can be heard only by dogs. A dog chaser whistle is quite effective with smaller dogs, but utterly useless when confronted with larger, aggressive dogs such as rottweilers or pitbulls.
Another tool you can use is a stun baton/gun or a pepper spray/gun. These tools are also very capable of protecting you against a human attacker. The former releases a small surge of electricity that can "stun" an attacker, while the latter releases a very strong (but harmless) chemical compound that can irritate the skin and stop an attack in its way.
Ultimately, the best way to prevent a dog attack is to be aware - avoid the roads where you know an aggressive dog lives, get away as soon as possible if you see a charging dog, and carry appropriate weapons with you.