I think they want to see employment separated specifically to see how many hrs you were working (presumably to support yourself) each semester/summer, because it's like a non-voluntary time suck. The option isn't there for the other sections of the app, so I don't think they care as much or necessarily expect you to chop up your activities.
That said, if I were you, I would list marching as 4 separate entries spanning the Fall semesters, as it seems more accurate. Plus, that way you can tweak the descriptions as you gained more responsibility, your hours/week look more significant, etc.