The local police could, as a matter of policy, refuse to investigate or enforce trespassing complaints where the act of trespass is access to a beach. In tandem with zoning ordinances barring the construction of new fences that restrict beach access, this could have the effect of providing public access to beaches without any legal changes to try to enforce that access.

What would likely happen from there is a combination of private prosecution for trespass (if possible; not every jurisdiction allows it), civil action for trespassing, widespread illegal fence construction and probably also refusal to comply with code enforcement orders, possibly civil action against the municipality to try to compel them to enforce the law, and active campaigning to elect someone who will change policy. It's an easy campaign, too - being "tough on crime" always sells well. Depending on the local attitudes, affected homeowners might also try to take matters into their own hands, potentially violently.