Thanks everyone for the comments. We did the excursion last week and it was good. We did NOT have to wear long pants for any portion of the excursion, and everyone was dressed in either shorts or bathing suits. You ride the hilly trails first then end up riding in the water at the end. Water shoes are recommended because then you won't have to take them off or change them before you take the horse into the water. It was 90 degrees that day and long pants would have been VERY uncomfortable. Please not that there is a 200 lb. per person weight limit to ride the horses. THEY WEIGH EVERYONE PRIOR TO BOARDING THE BUS. They bring a bathroom scale with them. If you weigh over 200 lbs., you will not be allowed to ride the excursion and your money will NOT be refunded.
The excursion was a little disappointing because while the trail ride was good, the ride in the water is short. They basically have about 100 yards of beach area near the stables, and you ride the horse back and forth in the water three times so that they can take photos of you. The photos will be available for purchase when you return to the stables. I thought we would actually tour the St. Maarten coast in the water with the horses, but that is not the case. They give you a free small rum drink (dixie cup size) when you are done, and they have bottled beer and rum punches available for purchase after the ride.
Not sure we would do it again for $99 per person.