An Idaho boy and his dog went on their daily walk up the steep hill behind their Pocatello home a year ago Friday.

Canyon Mansfield did his homework on this hill just east of town. Precisely 354 yards from the family swing set, the hill was home, and he and the 3-year-old yellow lab, Kasey, knew it like the pages of a well-worn book.

On this day, March 16, 2017, as he chucked a toy for the family’s trained hunting dog, he noticed something he hadn’t seen before. The teenager didn’t know it, but he’d stumbled upon an M-44, a…