Ok, this might be popular, or it might not be; but it can be helpful. In an area you suspect to have nails, staples, etc., just use any normal metal detector (thats right, the one you might take to the beach every now and then). It makes it really easy to find the nails, long staples, etc. in your backyard where dirt is the main surface composure, and where children might run through, or even where a vehicle might be parked. Mine (metal detector) sure came in handy when we had new shingles put on our roof. Got lots of staples out of the dirt, and a couple nails here and there. Most of 'em were either buried, or in amongst the gravel real good, wouldn't have known they were there. Saved some truck tires a lot of grief; and possibly a foot or two from the same. Hope this helps someone out.
-Patriot
P.S. A good magnet on a string, or even stuck onto the end of a metal pipe will help considerably if the metal object is near enough to the surface to puncture a tire. Just pulls it up through the loose dirt.