I primarily salt water beach hunt, and have used my Gold Bug SE on the salt water beaches here in NJ with very good results. In iron laden areas, where there are a lot of small, rusty nails and pieces of iron, the GB SE pulled silver and gold among all that garbage. Only bad thing is, it's not waterproof ! Some beaches, however, I cannot use it because it will hit on some of the thousands of small hot rocks and will beep and sputter every swing. If I end up turning up the discrimination to the point were I can manage, along with lowering the sensitivity, then it becomes small gold dead. It MAY find a bigger gold ring, but if I am in that situation, I just use a different unit.
Some of the higher frequency gold units won't work on the wet salt sand, because of the conductivity due to the salt water. The sand looks like one big target to them. On the dry sand though, they will work very well in finding small gold, but will also find every small piece of foil....which there are thousans of pieces ! There is an article by Tom Dankowski relating to micro gold jewelry hunting with a Fisher Gold Bug ( not the new ones that are out now...the 71kHz one). He states that you can find small diamond earrings, chains, etc. in the dry sand, but you have to use a small holed sifter and you will pick up every small piece of foil, bb, rivet, etc. in the process.
PI"s will not see chains very well if at all unless there is a bigger, heavier clasp on it. The small, fine chains are almost invisible to them. Where they excel is in the fact that salt water and mineralization have virtually no effect on them, and they can find the deeper, bigger rings, pendants, etc.
Fresh water hunting is a different animal, and I would imagine some of the gold dedicated units will be able to hunt them.
being good on finding small gold chains and jewlrey.