Either A) put your nasty, crappy POS bike next to all the other nice bikes and lock it up making yours look much less desirable or B) HIDE YOUR ****, MAN!

But...someone on here put it best...if someone wants anything, they are going to take it...just like a car. With modern technology this holds even more true. There are small, powerful, cordless tools that someone can walk around with, saw off a lock so fast no one would ever even notice and be gone looking like it was their bike the whole time. I've always kept high end stereo components in my cars with this knowledge always in the back of my mind. It held true for me once. I had about 400 bucks worth of stereo equipment stolen out of my car with another ~500 bucks worth of damage done to my car in the process a few years ago and I STILL am paranoid about my car. It gets better but it won't go away, man. It is a horrible feeling and, more or less the sole reason I would never do something like this to someone. You just have to do what you can and you have gotten every good bit of advice on how to do just that that anyone could ever want in this thread.