I believe the only exception to this rule is Military property. Coronado (off of San Diego) beach is an example. Eventually you hit the navy base...
I don't know about Coronado but at Dam Neck there is a fence that extends at least 150+ feet into the water clearly delineating the base. If the fence is not a dead give away there are signs every 20 feet on the fence that make it crystal clear that the other side of the fence is not a public beach.