Why not require your employees to take the time off? You could even schedule it for them at the start of the year "Bob, you're off the first two weeks of May an

Why not require your employees to take the time off? You could even schedule it for them at the start of the year "Bob, you're off the first two weeks of May and last two in October" and make it easy for them to reschedule to times that suit them, but not to carry over unlimited amounts of it.