He's in an area where everyone is rich. He's reasonably safe. His only real concern is fans bothering him. He's not that popular these days and his fan base isn't that young to be stalking him. As you've seen, he feels safe enough to be out running on the streets or walking up to get the mail.
Which begs to question, since there aren't fans driving around Malibu looking for him, are a few of them getting tipped off to be in the right place at the right time? Inside job, if I was exploring that question.
Out on tour, security is a different issue.