Is this the right way to do a Deposit to Hold a unit?

[Jared Miller]

I'm a landlord of 2 weeks.  I bought a duplex - 1 side came with a tenant. Filling the other.  I have a guy that looks great on paper, but doesn't want to move in for 30 days because he needs to give his current landlord 30 days notice, which, I completely respect him for doing.  Here's what I was thinking...Can I ask him for a deposit to hold now that will then be used as his security deposit? Can I also say It's not refundable if you decide not to take it, but will be if you do move in and then will be used as a security deposit?  Is this legal and a good idea?  I just want to protect myself from holding a place empty for 30 days and then he change his mind.