I would discourage you from using a debit card for a car rental. There are many issues, especially if the debit card is tied to your main cash account.
The problems range from locking out your cash in your account to if there is a problem with your rental, the company removing the damages from your account (rental car companies are authorized to do this).
I just rented one through Budget this morning. The site states that they will place a $200 "hold" in addition to the rental fees if a debit card is used. The amount will be refunded but only about 2 weeks after the rental is returned. I think we will pay w/a cc for that reason.