We did this in Grand Cayman on our last trip. My husband enjoyed it but my daughter and I thought that is very boring. I was ready to get off the horse 5 minutes after we started. I would have rather gone to a beach or do the sting ray trip. Big disappointment.
I just returned from a cruise with a stop in GC. Although, I personally, did not do this excursion, 2 people from our group did and thoroughly enjoyed it.
We did the horse back riding in Ocho Rios and we loved it. You actually ride the horses into the water. Not too deep though but the water comes to the top of the horse's back. It was very safe and definitely worth it. I would love to do that again, in Ocho Rios.