I have one word - Krytonite :
http://www.kryptonitelock.com/Pages/default.aspx They pride themselves on it & locked a very expensive bike somewhere very dodgy to prove their locks work.
For fixing within a shed / house then concrete a ring into the wall / floor to attach the bike to it.
I have <ahem> a few bikes

but fortunately have a secure brick outhouse & live in a quiet area.
For urban riding ditch the MTB shape and go for an old road bike with mudguards (you can put flat handle bars on it & change the stem to make it more comfortable / upright) so it's less attractive to thieves.
My rat (aka down the shops) bike is quite boutique if you can see past the grime, rusty bits and scabby mudguards.
Most dear is fire to the sons of men,
most sweet the sight of the sun;
good is health if one can but keep it,
and to live a life without shame. (Havamal 68)
http://gewessiman.blogspot.co.uk