Don the border collie drools excitedly as his owner, Malcolm Charlton, works with Nell, the family's female sheepdog, and a herd. Charlton and his wife, Mary Starr, have entered three of their five border collies in the working sheepdog trial at the New Mexico State Fair tonight. "It's kind of addicting," Starr says. "Once you get good, you want to keep going with it."