do you know any good metal detector ccomapnies that tell you how deep the metal detector can sense?

Answer 1

Check these sites...
http://www.garrett.com/hobby/home.htm
http://www.whiteselectronics.com/
http://www.tesoro.com/

Answer 2

It will all depend on the soil. In the California desert there is enough iron particles that u will be lucky if u can detect an object 6 in. deep.