U.S. Air Force Senior Airman Mark Cravens, 633rd Security Forces Squadron military working dog handler, and his dog Mmarc, 633rd SFS MWD, train to detect explosive threats at Joint Base Langley-Eustis, Va., Nov. 14, 2017. During training, the handler must guide the dog to make sure all areas are covered. (U.S. Air Force photo by Airman 1st Class Alexandra Singer)