LIFT YOUR COIL OFF THE GROUND - Another early tip someone gave me I still use to this day decades later. There's a couple of ways to use this technique. First small bits of shallow metal will try to head fake you, the machine may tell you its a deep old target when really its a shallow small bit of metal. If the target is truly a deep coin lifting your coil off the ground a couple three inches while sweeping a true deep coin will vanish. This has the effect of further increasing the distance between the coil and target e.g. depth plus Minelabs HATE air space between the coil and the ground, depth falls off fast on a deep target with just a bit of air gap between the coil and the ground. So lift your coil and sweep the target, did it vanish then odds are good its truly a deep target. But if you can still hear it with the coil lifted off the ground that's a smaller bit of metal that's shallow trying to head fake you.
Another reason to lift the coil is to confirm BIG deep iron giving a false high tone. BIG as in big old chunks of iron, an iron file, a horseshoe, BIG. These tend to be pretty deep and because they are so deep they can appear to be more the size of a coin than big iron. Also because they are larger than a cent the machine tends to incorrectly tell you the depth is more shallow than it really is (see above tips). If you lift your coil a few inches and you can still get a hit on the target, and lift the coil some more and its still there, lift the coil off the ground a foot and its still there, yeah big iron or trash target. Again a small coin size target 6 inches or deeper will quickly vanish when lifting your coil a few inches.
Shallow near/on surface coins and trash can head fake you. Your coil can detect these before you even get the coil over them, a few inches beyond the outer edge of the coil. The most common that I find are surface clad dimes tipped partially on edge in the grass and shooting a signal off sideways which throws off pinpointing, hence my bitter hatred of clad dimes LOL. For this reason and others I ALWAYS check a coil size area around where I think a target is. I want to be aware of any nearby targets, shallow or deep that may be interfering with my target. Nearby rusty nails for example, or near surface trash. If I find a particularly annoying near surface trash target, aluminum bottle cap for example and I think my target may be a deeper older coin I'll dig that trash target out of my way first then rescan.
For nearby rusty nails not only is it good to be aware of nearby rusty nails, they can shoot a false signal several inches off the end of the nail. If you get digging targets only to find there's nothing in the hole, just the end point of a rusty nail sticking out the side of the hole, there you go classic nail head fake. So its good to check a coil size area around a target of interest before you dig it. This also is educational, over time you will begin to notice a pattern of how nearby nails are oriented and their effects on a good target. That sometimes you will only be able to get a solid signal on a silver coin from just one particular angle, say north to south. East to west and all the angles inbetween SE, SW, etc. no target. Checking a coil size area around the target for nearby rusty nails you will find those nails are masking the target from other directions. This can get extreme, I remember one silver coin spill, two barber dimes and a barber quarter in the same hole, I could only get a signal on it with just the front 3-4 inches of my coil from just one angle. Any further forward nothing but iron, any other angle nothing but iron.
Why is this important? Because many sites have been well hunted for decades. The easy simple targets most of them are long gone. What remains are targets so deep the previous detectors could not get a signal on them, or difficult masked targets hiding in/under rusty nails and trash.