I've only been on two guided trips. One on the Bogey and one on the Columbia. On the Bogey I made mental notes on locations, stratagies and specific landmarks and wrote them in a journal that evening. I found that to be more difficult on the Columbia as it is such a large body of water. In that type of situation I think it would be a HUGE benefit to use a GPS to plot locations, as well as depth of water. I doubt a guide would mind if you are up front about it and ask in advance.