Professional "dog trainers" train the dogs to understand and comply with voice commands or hand signals. But as is more often the case, they find they must train the owners in proper use and technique. This is an important part of the dog training process if the trainer expects the owner to achieve the desired level of cooperation from his dog.
Dog trainers are not usually household names. Notable exceptions are National Geographics TV Personality Cesar Millan, who has recently catapulted to worldwide fame with his dog "training" abilities, Barbara Woodhouse, who had several series on UK television in the 1970s and 1980s and became something of a British national institution, and Paul Owens, who authored the best-selling book The Dog Whisperer in 1999 and DVD of the same name.