I take my dog anywhere and everywhere I go (other than work, but one of these days when I work for myself he will no doubt cruise there too).
The law states you must have your dog leashed in most areas, especially the fun areas we like to walk our mutts! But despite that, I let my dog off leash when I see it safe to do so. I would only reccomend this if you have a well trained dog that wont run off, or get too excited when it sees another animal.
There are many trails in the Laguna Hills, and in Newport Coast that provide excellent places to take your dog out. If you call a local bike shop, or a place like REI they will quite often have trail maps for the area. There you can find many trails for you and your dog. I would also recommend a book called "Best Hikes with Dogs -Southern California" that has some places for you to check out. Also look into trails in the mountains of Malibu, there are some amazing spots out there with waterfalls and amazing views. Hope that helps.