@Jen144, you are wise to ask about that.
The AirBnB "Security Deposit" is not really a security deposit. No money is taken from the guest ahead of time. If the host wants to make a claim against the security deposit, the host must make a claim in the Resolution Center, and it is up to AirBnB (and the guest) to decide if the host can receive any money from the Security Deposit.
So while with a normal Security Deposit, the host is in charge of deciding what happens to the money, with the AirBnB "Security Deposit" the host has no such power.
Maybe you can have the guest leave their Driver's License as a deposit for the parking pass? (Since while the car is parked, they won't need to drive?)