Use something like an air filled wall that has a base that extends 1.5 times as far as the height. It would be like a rounded L shape with the bottom part longer than the top if you were to observe it by looking at it sideways.
The front part of base would have to be slightly below the sand. Also additional supports would be needed behind the air wall to prevent it from sliding. The material which is filled with air could be plastic or vinyl etc similar to an air matteress.
The air wall would have to be filled less than capacity so that as the water weighs down on the base of the air wall the air moves to the other end of the wall or the backside which buffers the force of the wave via transfer of kinectic energy.
Wave Mitigation for Platforms or Water Crafts:
Same principal is used however the air ‘bladder’ would encompass the sides of the platform or craft and somewhat underneath and the air would rush from one side to the other as the wave pressed on to it.
You could then channel the moving air away from the water by some outlet or series of check valves or one way valves to prevent teetering and sub waves.