Aaaahhhhhhhh, the old rusty nail problem

I use a Fisher CZ-3D. All of the CZ's are more alike than different. Here's the thing, Fishers in general tend to love iron - especially older, deeper iron. The CZ's are some of the deepest detectors out there. They can rival - if not beat - Explorers, T2's, F75's, etc. The trade off of course, is the iron problem. They like to give a high tone on junk.
There are a few tricks you can try to 'ferret' out what the target
really is before digging. However, these tricks aren't perfect nor do they work everytime. But, it WILL cut down on some of the iron.
1. When you get a deep-ish high tone that you suspect might be iron, try raising the coil about six inches above the target & see if the signal or tone changes.
2. Try flicking or whipping the coil over where the target signal is. This sometimes reveals the true identity of the buried item.
3. Listen real close to the audio. It's difficult, but, after a while you'll be able to pick-up tell-tale signs of iron.
4. When pinpointing or X'ing the target, iron tends to have a very wide field. It covers a bit more ground. Very diluted. A coin or ring on the other hand has a very tight & narrow signal. More zippy too.
A lot of this probably doesn't make sense, but, it will after 100 hours or so on your detector. IMHO, CZ's aren't the best choice for trashy/iron laden sites. They'll work fine, but, you're gonna have to slow waaaaay down & your trash to good finds ratio will be through the roof
Good luck!