Are you looking a putting something small in the ground, like you would open the top and work on it or a ROOM that has stairs and a lot of dirt on top so there is no sign form the air? The room idea is a dream of mine, notice I said dream...Here are some links for the latter.......JR

Get out the wallet
http://www.hardenedstructures.com/underground.asp

This one is way more survival but you can't tell your neighbors your building a room to grow weed in can you
http://www.alpinesurvival.com/nuclea..._shelters.html

Or move to Tennessee and live here (Don't jump on me I know it sold already)
http://www.youtube.com/watch?v=Hg2TyjWjCls