Non-refundable deposit to reserve a rental?

[Nate Chucta]

I have a student rental that is currently rented out until 7/15/2017 and I'm already fielding quite a bit of interest for people who want to sign a lease for the 2017-2018.  

I'm a new landlord so I'm curious how others have handled situations like this.  Do you ask for a non-refundable deposit right now to reserve the home for next school year?

Or do you just have them sign the lease for 2017-2018 and get their deposit as normal.  If they break the lease, then I would assume I could keep their deposit, right?

Thanks for your help!