I'd say ditch the keys and get a good lock with a keypad. That will eliminate the need to keep up with keys and always having to ensure guests return them and don't lose them or take them with them, etc.
I'd highly reccommend this new lock we recently got! It syncs with your AirBNB calendar so each time a guest books a stay with you, it automatically sends them an email confirmation with their key code. It auto updates itself and auto switches codes for you when guests check in and check out! Saves me a whole world of time and makes hosting not only super easy on me, but easy and convenient for our guests!
Here's a link to it for you to check out:
https://www.amazon.com/AirLocking-Smart-Lock-for-AirBNB/dp/B0759NPC5Y/ref=as_sl_pc_tf_til?tag=airloc...