Hi, has anyone had luck with using sand as the beach/shoreline medium? I'm worried about it washing into the pond when it rains. I think my slope at the steepest is 3:1. I'm torn between using sand or a 10mm (1/4 inch) round rock. Any advice is much appreciated.

Put geotextile fabric down before you put the sand/gravel down, it will minimize the amount that gets incorporated into the soil under it over time.

You can run that geotextile fabric into the pond, over a horizontal line of cinder blocks to help "trap" the sand that goes down slope.

My parents have a sand beach that was built by the previous owner in the 80's and still looks nice. It is almost flat on land with at least 4" of sand in the actual beach area and the slope once it reaches the water is very low, maybe 4:1.