Babysitter Needed - Full-time / Part-time

I am looking for a great nanny for 2 children in San Francisco. I would prefer a nanny who has their own car, who does not smoke and who is CPR certified. I have the children 50% of the time and they will need care while I work during the day from when their camp ends July 22 until their school begins August 25th either 2 or 3 days per week. They are lovely 5. 5-year-old twin girls and love to play in the park and forests of presidio and GGP.