To become a sentinel at the Tomb of the Unknown Soldier in Arlington National Cemetery, Army soldiers must endure a six-to-nine-month training program that 90% of trainees do not complete. The sentinels say they’re constantly chasing a standard of perfection. No one feels that more than 19-year-old Pvt. Joshua Beckman, a tomb guard training to be a sentinel. We met Beckman as he rigorously prepared for the uniform inspection test, one of five tests the trainees must pass to attain the coveted