Well, here's what I was going to do, but had to scrap.
Gather the items you'd like your detector to "see" in the ground. In my case, I hunt mostly coins so I geared my garden to that. I planted a silver quarter, silver dime, war nickel, buffalo nickel, IH, couple of wheats (one vertical), pull tab, lead bullet, zlincoln and a gold ring. I spaced them all about 1.5 feet apart from each other in a straight line. How you configure the layout is totally up to you, this arrangement worked for me. I buried all these items between 7" and 8" in depth. The reason I did this is because I wanted to configure my machine to find coins at that depth or deeper. Where I am, I can (and have) found coins and relics around 8.5" to 9" deep.