As a former trail guide from a hack stable, I would imagine it is lead by guides. They will probably let you run in certain areas, then swim, then will let the horses dry for a while before putting the gear back on. I doubt they'll let you go off on your own. I'm sure it's more geared for the novice, but still a fun time. I just know the saddle sores it can cause on the horses, so feel bad about doing it. Plus, I really don't like the presents that horses leave in the water
I haven't ridden at Half Moon Cay, but have a feeling that's how it would be run. We did a ride in St. Lucia, and they had 4 guides with us.