There's not a single beach in CA that you CAN'T detect, barring a few "supposed" federal beaches. And I'm assuming "Marina Del Rey" is simply city, county, or state (and not federal). There's no "permits" for ANY beach in CA. No ones ever thought to ask, thank goodness. So ........ we all just leave good enough alone here, and ........ no restrictions, etc... I'm sure if you asked enough bureaucrats in whatever locale your going to "can I?", that you might not find someone to say something wierd. But *realistically*, you can detect any beach here till you're blue in the face, and no one cares.