Have fun - last time I was in coz - we rented a Jeep and thank god I was with a male, becuase we had to change the tire in really deep sand, of course we were gong where we shouldn't of!
if you rent a vehicle and you want to snorkel, go to the beach just north of Fiesta Americana hotel - that's where you will find the best views and then you can come up to the hotel, have a drink and do it again - the current flows towards the hotel.