When I go kayaking I like to hang my car key around my neck on a piece of string. You wouldn't want to do that with the standard key as I'm sure it's not waterpoof.
I just got what I expect should be a waterproof key from Mister Minute for $150. No remote function, but it unlocks the door manually and starts the car. As far as I know the chip for the immobiliser is a sealed unit so it should be waterproof.