Acrylic   40X50 cm
He is drawing  Kia kaha  (stay strong) symbol in the sand but the tide will come in and wash it away.
 
Kia kaha is a Māori phrase used by the people of New Zealand as an affirmation, meaning stay strong. The phrase has significant meaning for Māori: popularised through its usage by the 28th Māori Battalion during World War II, it is found in titles of books and songs, as well as a motto.