Some dogs seem to regard bicycles, motorcycles and yes, skateboards as entrees on the run. Three-year-old Shepherd mix Simon enjoys napping on the sunny spot in the dining room, tossing his Wubba, and playing with his friends at the dog park. His favorite sport, however, is chasing anything that moves. Lately, this includes not only motorized vehicles, but also hapless joggers and even strollers. His owners suspect that an early run-in with a tricycle may have caused his obse