<span>Sand dunes move because of wind, so to prevent a sand dune from moving you need to either: stop the wind; or stop the sand dune from being able to move. For example, on beaches, sand is stopped from moving by using groynes, which physically stop the sand from being carried any further along the beach
(Copied from my comment, pasting it here because I know on mobile apps you can't see comments, so if anyone searches, etc.)</span>
