Yes I had them sit very still this was 1 of 7 shots I took of them on the rock, they were very cooperative I also used a flash on a 2nd curtain sync.
Here is another shot of the same couple from a different angle. You can see when the flash went off it caught a splash in the water by his left foot. I edited it a bit in photoshop to give it a slightly out of focus look, I thought it softened up the picture a bit.