Duke certainly lived the dog's version of the American dream. In less than a year he went from life in a Tracy pound to the life of a top-notch Pleasanton police dog. The slim, good-looking German shepherd was rescued by Pleasanton officer Tim Martens in spring 2000. Originally, he was supposed to be a family pet, but Martens sensed Duke would make a great police dog.  After passing handler and police dog classes, the pair joined the department's canine team in fall 2000, said Lt. Tom Fenner, manager of the department's canine unit. "It's very unusual," he said. "It's the only case I know of where a rescued dog from a pound becomes a police dog." A few weeks ago, Duke had trouble eating and began losing weight rapidly. Medication didn't help. Then a veterinarian discovered intestinal inflammation that probably had been developing for months. Martens was in the midst of seeking a third opinion at UC Davis' veterinary clinic when Duke had to be rushed to an emergency clinic and put on IV. He died Thursday, only 6 years old and in the prime of his police career, Fenner said.  Duke was known for his ability to find illegal drugs in vehicles and homes and on people, Fenner said. He was so good that other agencies, such as California Highway Patrol and the Dublin and Livermore police departments, would specifically ask for Duke to help them out on cases.  He also protected police officers. Last year when a car chase suspect refused to come out of some shrubs, officers had no idea whether the suspect was armed. Martens let Duke loose, and the dog brought the suspect out. He was handcuffed without incident.  "Duke did exactly what he was supposed to do," Fenner said. "He protected the lives of those  Now down to two canine units, Fenner has the task of finding a new dog. The department has funds set aside to purchase and train a new dog.Those who knew and worked with the Duke, were saddened by his untimely death, Fenner said. "He was an extended member of our police family," he said.