Any machine will fool you on iron sometimes. Just the nature of the best in detectors, but I will say if I choose not to dig iron I can pretty much spot a false iron coin hit. With more experience you'll learn the suttle sounds, VDI, and other traits of iron. It often has a ghostly sound to it even when giving a coin signal, and will not repeat as easily often, and will usually null all the rest of the way around it. But, you've got to dig those "iron" signals when they pop up and hint with a coin high tone in order to learn what could can can't be a possible coin. Even still, at a pounded out site I'll dig the signals I'm sure are iron giving a false coin hit because no machine can always tell you for certain it's iron and not a badly masked coin. With time you can weed out the ones you are sure are iron, but many are borderline and still yet even the ones you "know" are going to be iron might be actually a coin. The Iron Mask feature of the Sovereign has me digging way less iron than I ever did on other machines, but even it can get fooled here and there. That's when you have to use your ears and eyes, as that should always be the final factor it what you deem dig worthy.
Some people will switch to pin point mode and see if the "coin" moves, and often that indicates it's iron. I don't like trusting that myself, because pin point mode could be dragging you away from a real coin and showing you the nearby iron, making you believe it's a false coin hit. I prefer to use my ears and my eyes (does the VDI climb in some form of fashion or is it bouncing around randomly, indicating probable junk).
