If it is possible for this group to learn anything they will learn from the Dutch to NOT depend a a dike. The Dutch have a defense in depth strategy to live with the water not against it and redundant dikes and tons of low-lying farm land that can be intentionally flooded. They would dam off the Rigolets for one thing.
Low lying farm land, sports fields, parks, recreational areas, golf couses...might work below sea level.
But homes, commercial offices, casinos, hotels...with lots of people below sea level is asking for trouble.