Took Gymdog to Cornwall over half term and he went to a beach for the first time (well, first time since I've had him).
He LOVED it. We found a perfect starter beach for him, small, shingly, very few people or other dogs. Initially all he wanted to do was chase stones in the shallows which was fine and seemed like great exercise.
Then he started something else. With his paws he would feel out a large rock half-submerged in the sand under a foot or two of water. He then dug and dug at the rock and moving backwards pulled it right up to the shoreline. These rocks were HUGE! Massive things - bigger than his head. He would then attempt to fit the massive rock in his jaws, take it carefully right up the beach, drop it, immediately lose interest and go back and do it all over again. The zillions of pebbles and rocks actually on the beach were of no interest - only those monsters half submerged in the sand and under the water.
After a while I realised Gymdog could end up having no teeth left at the end of the holiday and tried either to distract him or help him carry the ludicrously large boulders. He wasn't having any of it, he was clearly on a beach clearing mission. His claws are nicely filed though!
So does your dog have any beach-specific behaviours?