For spain, most of the companies will want a credit/debit card as a form of security toi satisfy the insurance. There are lots of scams in Spain that involve theives posing as rental attendants who park your car for the hire company. Instead they steal the car but if gave them the keys then you are liable.
The rental company will charge your credit card for the cost of replacing the car. Similar stories were on watchdog last week, you might even be able to catch it on BBC media player.
Joe Blogs