Here's another tip:
When setting discrimination (or notching), most people only accept one or two numbers on each side of the target. For example - nickels normally VDI at 20, so most folks will accept 19 to 21. However, doing so will result in poor audio response for the target. In order to maximize the audio response, you need to accept plus or minus 5 to 8 VDI numbers. So for nickels, you would accept at least VDI numbers 15 to 25 or 12 to 28 (12 to 25 works too etc.). The downside to this practice is that it exposes you to digging more trash than the other method. It is up to you which is more important, really good audio, or relying on VDI numbers for target ID.
Personally, when looking for deep, high value targets, I set my VDI to maximize audio response. If I am moving fast, looking for shallow targets, I set my VDI discrimination to accept only nickels, dimes, quarters, and dollars. Rej. -95 to +19; Acc.+20; Rej. +21 to +77; Acc. +78 to +92; Rej. +94,+95.