Buy a cheap pair for the beach.

Yes. That is the main move. Keep your nice sunglasses at home and grab a $15 pair from Target or Amazon for pool and beach days.

Sunglasses get scratched by sand, dropped in the water, knocked off your face, or left on a towel while you swim. Even a good case won’t help if you forget to use it or leave it open. Cheap pairs look fine from a distance and make you stop caring. When you lose them, you shrug. When sand scratches the lens, you shrug.

A lanyard or floating strap helps, but it only solves the “lost” problem, not the “sand-scratched-to-hell” problem. If you must bring nice ones, keep them zipped inside a hard case buried in your bag and only wear them on walks to the car. But honestly, just buy cheap ones. It is not where you flex your sunglasses.