OT a bit, but a quick, hopefully humorous story (I'm never quite sure....LOL) about the "marching while home on leave" thing...
1970, my older brother Lenny was with the Manville, NJ, Sacred Heart Crusaders junior corps.... my dad, myself, and Lenny's twin brother Marty went to see them at the World Open in Lynn, MA. Marty was with the Air Force and was home on leave.
Lenny and Marty were identical twins. Really identical. Unless you were immediate family, you could not tell them apart back then.
Long story shorter... at a nighttime rehearsal up there in MA, Marty snuck into the drill in Lenny's spot... of course, Marty had absolutely no idea what the drill was.... and for a period of time drove the corps' director and drill guy crazy, until the switchup was revealed. LOL.