JD, what you're referring to is a pre-authorization, which is automatically done by some establishments when the card is swiped. In the case of a gas station, since the amount of the purchase isn't known until you finish pumping, some will pre-authorize the maximum amount of gas that they allow to be pumped, which in many cases is $100. Once the final charge amount is determined and charged to your account, the pre-authorization falls off.

What this car rental company is doing is different, and if it isn't removed until ten days after he returns the vehicle, then his card will in fact be limited by that amount, in addition to the amount of the actual charge, until they release the hold

Personally, I wouldn't patronize a company that does that. There are plenty of rental companies on the island that don't put holds for possible damage on credit cards.