The barriers are usually gated walls/fences. The right-of-way is likely quite small and nothing prevents a property owner from walling off his/her land from the masses. Likely, the gate across the right of way is put up appropriating the ROW for the property owner's own benefit. The police will not break down the walls or gates, but they likely will cite the property owner, but for those guys, a citation is nothing. They'll pay them ad nauseam because they're not criminal in nature and are chump change. The only way to get the gates down is to file suit like Surfrider did.