I changed to giving short "live" chair placement playoffs (4-8 measures) weekly, Sometimes I would dedicate a day [Thursday, for example], or have a section or two each day of the week. This would be random and not announced until the day of. That way the same section wasn't always doing theirs on Monday, or having the luxury doing theirs all the time near the end of the week. The assignment was given the week before, so all of them had at least the weekend to prepare.
I know this took away from valuable class/rehearsal time, however there is no substitute for playing live in front of their peers as opposed to submitting by recording on-line.. Many times the material was from the music we were releasing, or Regional audition music.
I saw an increase in practice and improvement without the question of whether the records were "accurate". Also, in the live setting, there was no hiding if the student was unprepared.