The iron problem has been since the beginning of the hobby and will be to the end.
Like Sandman mentioned, the Minelab product is about as good with iron as you're going to get with a deep seeking machine. That is, if you wish to not even hear the iron.
If you don't mind hearing iron, then the Nautilus IIb or IIba is the machine. The Nautilus DMC system gives two signals simultaneously (all metal and discrimination).
No detector made can see right through iron like those kid's X-Ray glasses of the 50's could see through a girl's dress
The old coin under the nail trick can be done with most any lower quality detector. I have two cheap Chinese units that can do it just as well as any Tesoro. Your higher quality machines like the Minelabs sometimes won't do it due to the iron mast settings.
So, as of today, the best thing to do is dig it all if you really want to clean a location out. I dig it all with the detector and if the site is hot and I can make a mess I'll dig the rest with a shovel and screen the dirt.
If digging all isn't practical, then you know you're going to miss targets. The best strategy then is to use a top machine and a lower level machine at the same site. The Explorer or GT followed by a one of the Tesoros is a nice combo. The Minelabs will almost totally ignore iron but the Tesoros won't pass up large iron. So, the Minelabs will grab all those in-between targets (between large iron chunks) and the Tesoros will remove the largest pieces of iron but will leave those millions of tiny fragments behind. In so doing you'll find more good targets.
Make sense? If not have Sandman translate all the above for you (especially the part about the X-Ray glasses)
Badger