As far as residents knowing about this, they hold meetings that discuss the exhibits of how they want to make sure they are away. However, building these sea walls takes sufficient time and effort. Sometimes the walls may collapse due to poor structure or environmental abuse such as heavy waves, walls collapsing, and wall end failure. As we would assume for quality sea walls it is more on the pricer side than affordable depending on the island's economic status and views regarding building stable sea walls.
http://henge.bio.miami.edu/coastalecology/windermere/Sea_walls_2006_condensed%5B1%5D.pdf