The pro coil is fine in rusty iron, I have hunted rusty nail hell holes with it. If you hit the nail at the right angle, or more often than not catch the nail with just the edge or front/rear of your coil it can false. Its important to get your coil centered over the nail for accurate ID of iron. Its important to turn 90 degrees and sweep it again. Its important to check a coil size area around where you think the target is, often you will find your signal is actually a nail a few inches away. Its important to watch the bounce pattern for rusty nails, its a classic pattern repeated by no other target, credit to Mike M if memory serves. The rusty nail bounce pattern is between upper left edge of the screen to upper right edge of the screen on a slight downward angle left to right. I have dug many of those signals just to confirm and they are always rusty nails. If you see that bounce pattern you are pretty much guaranteed there is a rusty nail down there. The thing to watch out for are mixed bounce patterns, bounces to coin locations mixed in with the rusty nail bounce pattern. If its sometimes bounces to a silver dime location, cursor half off the top of the screen, or the indian head location you may have a coin hiding next to the nail. Be advised rusty nails can throw a signal a few inches beyond the end of the nail along its length (sometimes goodies hide under this iron umbrella). The wetter the ground the bigger the umbrella which is why I go back later when the ground dries out. The old Minelab 8" DD coil which is really more like 7" has made some finds in thick nails that proved too much for the larger Pro coil.