My suggestion is to sell them to Ben Shapiro
Did they just dump sand in a big pile? Sand dunes are pretty well-understood ecosystems that require something underneath to anchor to as well as plants on top to stabilize them.
But also, the ocean is going to continue to rise, so any effort is likely futile. Sorry about that dude’s tennis court getting ruined
So what your saying is they should have put the tennis courts on top of the sand dunes to stabilize them.