Trainer uses attack dog to show letter carriers how to avoid getting bit "To show just how dangerous dog bites can be, the USPS brought in a professional dog trainer to demonstrate how to prevent attacks. Hector Hernandez, known as “Canine Man,” is a speaker, trainer and author who gives demonstrations throughout the country, but has been working with the USPS for the last 20 years. He trains new letter carriers in how to defend themselves against dog bites."