My current strategy is to be as flexible as possible up front, but track who is consistently calling out/late etc. Then energy gets devoted to having meetings with them and figuring out what is going on. My thought is that you'll always have someone occasionally game the system regardless of the system in place, but you'll find out quickly who is looking to take consistent advantage of you by looking at the patterns. It's kind of like how Amazon will almost always refund your order if you claim it was lost or stolen. But if you make this claim once a month, they just shut down your account.
