Wow, people steal seats and derailers, i'm lucky i live somewhere where theives wouldn't go to that ridiculous extent. Any how, i have a twisty springy chain type things that i hook around the front wheel, frame, and thats about all. Its good because it is hard to quickly remove off the bike. I leave my bike in public so it is less- likeely to get stolen, and anyone could take my seat post off, but no one has yet
. I guess if you live somewhere safe you need not worry about these things.
If someone wanted they could unscrew every little thing off the bike and vertauly get away with everything but the frame, but i dont know anyone who would?