In my opinion, the point of having a lock is at least as much about the appearence of security as about the actual difficulty of opening the lock.
If someone really wants your bike, I don't think there's anything you can do about it, but if it seems like the bike next to yours is easier to steal, then the thief will take that one, and not your bike.

I think it would be really difficult to achieve that appearence with a home-made lock.