A few ways you can do this.
Disc 6 and Monotone is Dankowski's suggestion for hunting in iron and it works in mineralization pretty well also.
Others use 3 tones, 0 disc and listen for that good, repeating solid sounding higher tone, or lower tone for some targets like nickels.
I use something I call the blast through method for hunting in difficult sites like this.
Works great in iron oxide mineralization or sites with a ton of iron which you might have there, other kinds of minerals I don't know but both these methods might work well in other places too.
If it is iron you are dealing with these units will up average all targets around that so be aware of this.
Hot rocks can sound real nice and I deal with them all the time along with red clay mineralized dirt but most of them will generally act like iron where they might stay high but ultimately will drop down low on some passes or if you turn and hit them from a 90 degree angle.
Coins and good target usually will stay in the higher ranges for me with few if no drops low from any direction.
That blast through process takes some time to learn and get used to but worth the effort and the best way I have learned to pick out masked targets in challenging sites.
Use your all metal setting where you can control the threshold then max out both the gain and thresh.
Listen to the tone but watch the screen closely.
You can try boost but DE is faster and better for picking though junk, move the coil very slow, look a range of numbers that stay high on most passes, that range can be from 5-8 numbers.
If the numbers drop a lot probably not a good target.
Use your pinpointing function to make sure the spot you are swinging over is where the target is and not repeating falsing from iron or other garbage in the vicinity that might be near but not even under your coil.
If you have the spot with that repeating range on short quick passes turn and hit it again and if you get the same behavior without much dropping dig that signal.
The hardest part about his is training your brain to notice that block of higher repeating numbers when you pass over a good target because in all metal you will see and hear everything and things can happen real quick.
Many use all kinds of ways to do this but after I put in the effort to learn this method it has given me the greatest amount if success in many different sites for the last few years but others use different methods entirely.
More about this method in this thread plus info about up averaging around iron.
http://www.findmall.com/read.php?37,2322233,page=1