I really think they all should put up a fence. I think that this would be a good negotiation but have the city pay the fencing since they are causing the problem.
I'm pretty sure that every property along this section has on the deed specifically stated that they are building or buying property that is up against a public beach, and further notes that they can't restrict access to that beach. The problem isn't the city (or the California Coastal Commission), but private property owners who ignore what they signed and agreed to and treat public property as if they own it.
They've painted curbs red, put up fake no-parking signs, put gates across public access lanes, and now hired guards to chase off visitors to the public beach. That most of these homeowners are liberals is likely the only reason why the DA hasn't filed charges against them.