Along the coastline of the United States, such legal rights have served as ammunition in an increasingly acrimonious war pitting the public against owners of extremely valuable beachfront property. Without performing thorough due diligence, those considering buying coastal real estate or property that abuts public land may unwittingly find themselves locked in expensive legal battles. Victory for landowners is hardly guaranteed. “You don’t want to pay $20 million for a beach house and find out you have to allow the public to walk through your yard,” says Elizabeth J. Giffin, a land use attorney in Los Angeles.

Nowhere has this struggle been more contentious than along the 27 miles of coastline that make up Malibu, Calif., the famous beach city northwest of Los Angeles. The most high-profile case involves David Geffen, legendary music producer and partner in DreamWorks SKG studios, who has been in a protracted legal fracas to prevent the establishment of an easement across his Malibu estate down to the sands of Carbon Beach.

A few miles away, on Broad Beach, the Trancas Property Owners Association has, in the past, employed security guards on ATVs to chase off sunbathers and surfers who turn into trespassers by going beyond the mean high-tide line—the mark where public property ends and private beaches begin in California. Last summer, the battle for beach access grew so heated that the California Coastal Commission, the state agency charged with maintaining the Golden State’s beaches, ordered homeowners to disband their security force and take down some of the many no-trespassing signs. The agency even published an online aerial map that showed each homeowner’s plot, noting any lateral easements that allow the public to use the beach above the mean high-tide line. The property owners association has sued, and its case is currently pending.