Ocho Rios as stated is not a place to venture on your own. You'll realize it the minute you step off the ship and are mobbed by the locals. They are very aggressive, even on the pier. Don't carry large amounts of cash or anything that may be percieved as very valuable. Leave the Rolex in the safe or at home.
The falls is fine... once. After you try getting out of there at the end you'll be so happy to get back to the ship. I got lost in the mob in that market the first time there. Paid a local $20. to point me to the exit and to the ship. Would have paid $200. to get out of there.
What a shame that one of the most beautiful islands in the world is so poverty stricken and corrupt you can't enjoy visiting without a hassle.
Happy sailing, Neil