I am under the impression that GPS systems aren't allowed on trips like this.
And they would search my dry bag? I always carry my GPS with me for several reasons. Not to mention that my phone has one built in as well. Many modern phones have it and it would not be practical to determine which one is ok which one is not.
As I said, I don't care about this but I do log coordinates of my every dive site in my log and am going to continue to do so.
If the dive operation treats me as a valued customer I will continue to come back. If they treat me as a suspect even before I get on board then I'll want my money back and go somewhere else.
Plus if I were a rival operation, it is not that hard to follow a boat going out and track it on the radar from a distance.
What I am saying is that there are easy ways to find locations if one is really interested in stealing "trade secret".