use the learn feature on the machine. it is explained in the manual. you can "teach" the machine to only accept the items that you scan into it. personally im not quite sold on this feature yet because in my mind a target might ID differently in different soil conditions but some people swear that it works great.
I wouldn't want to narrow it down too much. Maybe I should have it learn to reject clad? Mostly pennies, some dimes, & quarters. I don't have many gold & silver items to learn with.
I do have a list of gold & silver (coins) #'s. Should I accept the whole "silver spectrum" from the lowest to highest ferrous & conductivity & ALL NUMBERS IN BETWEEN?
the problem with having it reject clad is that clad rings in in the same spots as silver does. you could probably set it up to ignore zinc pennies, but dimes ,quarters ,halves and dollars being rejected would also null out silver.