My recommendation would be a day cruise on the Celine Too. Neil, the captain, would take you to a deserted island called Tintamare where your son would have the perfect setting for his proposal. Afterwards Neil will prepare a delicious cooked meal for all to enjoy on board. More stops along the way for snorkling, an open bar all day and a return at sunset. We have done this many times in the past and it is the best day of our St. Maarten vacation!