When Andrew van der Merwe began drawing designs on sand he used a stick, but the result of that was messy markings on the ground. So over the course of ten years, he has developed his own instruments to scoop sand which allow him to create crisp v-cut letters and more. You can view his painstaking carving-process in the video at bottom of post.
Top: Photo © Anja Wiehl and Andrew van der Merwe.
https://www.youtube.com/watch?v=iJgSerUGmuE
Bibliography: van der Merwe, Andrew. "Wor(l)ds Project Report–Beach Calligraphy." J-Laf.org. October 21, 2008. All photos © Andrew van der Merwe Via Behance