Seriously, I would speak to a legal advisor to see if I could create a contract of liability that who ever rented my car would be stuck with the ramifications of their actions.
Essentially, I would own and insure my car as the law requires but while their in possession the contract would dictate that all responsibility would be on their shoulders/insurance. Of course I have no idea if this is possible but if i were to consider it, my first stop is legal council.