Excal 2 does pretty good recently found a 23 inch 23 gr 14K with nothing attached to it and it rang out nice and loud. Was down about 8-10 inches (1 big scoop)
I think Tesero might have the market on this one, I have heard the Tiger Shark is great on small chains in the water and your first reply also stated a Tesero. I know my Explorer is not great in this area unless the chain is large or has a charm on it. The links make it hard for most detectors to give a good signal. Just my opinion!
on air test the dfx easily picked up fine gold chain the excalibur did not register. The Beach Hunter is essentially the same as the dfx; not sure how well they do on chains in a saltwater environment