this is probably more for things that people won’t bother stealing. I certainly wouldn’t be trusting my phone to it.

I’d also be worried about it getting covered and misplaced/lost. piles of sand look much like another.

Could be a fun geocaching thingamabob, though.

Edit: I’d also suggest sticking a silicone o-ring on the lid. you can make them pretty easily using fish tank air-hose tubing. Pump it full of calk. If you want a solid ring, let it cure, then blow it out with an air-blower nozzle on an air compressor. If you want a hollow ring, which for this would be best, I think; blow out the tubing before it sets. then blow it out again. cut the ends on a bias and then glue them with more calk.

For this, you’d never know when a kid comes running over with a giant pale of water.