pop-culture icon, with her emphatic "sit" and catch cry of "walkies" becoming part of the popular vernacular. The monks of New Skete, who were breeders and trainers of German Shepherds in Cambridge, New York, published How to Be Your Dog's Best Friend: A Training Manual for Dog Owners in 1978 and it became an immediate best seller. Despite advocating a philosophy that "understanding is the key to communication and compassion with your dog", they endorsed confrontational punishments which were later shown to elicit dangerously aggressive responses in many dogs. In the 1980s veterinarian and animal behaviorist Ian Dunbar discovered that despite evidence on the peak learning periods in animals, few dog trainers worked with puppies before they were six months old. Dunbar founded Sirius Dog Training, the first off-leash training program specifically for puppies, which emphasizes the importance of teaching bite inhibition, sociality, and other basic household manners, to dogs under six months of age. Dunbar has written numerous books, and is known for his international seminar presentations and award-winning videos on puppy and dog behavior and training. Prior to the 1980s, Karen Pryor was a marine-mammal trainer who used Skinner's operant principles to teach dolphins and develop marine-mammal shows. In 1984, she published her book, Don't Shoot the Dog: The New Art of Teaching and Training, an explanation of operant-conditioning procedures written for the general public. In the book Pryor explains why punishment as a way to get people to change often fails, and describes specific positive methods for changing the behavior of husbands, children and pets. Pryor's dog training materials and seminars showed how operant procedures can be used to provide training based on positive reinforcement of good behavior. Pryor and Gary Wilkes introduced clicker training to dog trainers with a series of seminars in 1992 and 1993. Wilkes used aversives as well as rewards, and the philosophical differences soon ended the partnership. 21st century The 21st century has seen the proliferation of television programs and accompanying books that feature dog training and rehabilitation, including Joel Silverman's Good Dog U, Dog Whisperer with Cesar Millan, It's Me or the Dog featuring Victoria Stillwell, The Underdog Show, Dogs in the City, and SuperFetch. The Association of Pet Dog Trainers advises that television programs are produced primarily for entertainment, and while all programs will have good and not-so-good points, the viewer should critically evaluate the information before deciding which training