We had the same problam two years ago at my school. What you have to do is just play your part and hope that the rest of the line will fallow in your example

Leadership is action, not position. You don't have to be a Band Director, Caption Head, or Section Leader in order to make a difference. Also, too many times people equate discipline with yelling and 'putting someone in their place'. Quite often, a group of rowdy kids will respond more to someone who doesn't yell at them, but rather explains WHY things need to be a certain way. If that fails, then possibly the Band/Corps probably isn't the place for them.