Not getting back the ship in time is always a concern. If the independent tour is an all day tour 6-8 hours, I would not chance it and just take a ship tour. But in this case, the tour is only 2-3 hours. The distance from the old town to the ship port is a short one. This tour uses private vans, and the tour does not rely on public buses. Dora is well aware of the time constraints of those on the ship. I had no qualms about booking Dora. She got us back to the ship with ample time. We had more than enough time to peruse the gift shop at the port. So I wouldn't worry too much on this trip. But, having said that, we always carry our passports in our money belts when we take excursions, ship's tour or third party tour, just in case.