Climate change, here we come :-(

I almost forgot to say that if you have a car you should try to go to the Roman ruins of Belo Claudia near Tarifa. They're not Spain's best Roman ruins, but they aren't bad either and they are easily reachable by car, but not so reachable without one.
Beach in Bolonia is gorgeous.. And I don't use that word very often :)
Global warming here we come... and I've been flagging off the Ave so relentlessly.
Becky - renting a car in Jerez is a good option. The road around Tarifa will be busy in the morning around 11, lunchtime at 2pm - 3pm and in the evening at around 8-9pm. Off and on the beach traffic. It's a good road though, and quite picturesque. There is a new A road from Jerez through Puerto Sta Maria so you do not have to do the N-IV on that bit, which is nice as it's a miserable bit of it. If you decide to rent the car at Jerez airport, let me know. I'll PM you good driving directions. Note: the airport is some distance north of Jerez and you do not go into town on the way out. Do not follow the signs to Jerez - take Cadiz/Algeciras direction.
