This is, unfortunately, one of those battles between warhead and armor, and unfortunately, the warhead almost always wins.
Don't lock the door? Somebody waltzes in and takes something. Lock the door? Somebody opens it with a coathanger and takes something. Make the locks jimmy-proof? Somebody hucks a rock through a window and takes something. Spend piles of money to replace the windows with unbreakable Lexan? Somebody finds out they can't get in easily or quickly, so they set fire to the whole car. Fill the car with alarms, fire-suppression, and set up a surveillance camera? If somebody wants it badly enough, they'll drive by with a stolen towtruck and take the whole thing.
As far as a car goes, the only reasonably sure cure is an enclosed garage attached to the house, motion-detector lights, an unfriendly dog, a light sleeper and a large handgun.
The best defense is to not look like a target. An '87 ElCamino is hardly a top-lister of stolen cars, and will be largely ignored by crooks unless it's got fancy paint, shiny wheels, or other flashy accessories.
And sad to say, but nothing will protect a high-dollar stereo of the crooks really want it. If they want the whole system, they'll steal the entire car. Ignition lock or steering-wheel club or no. Chances are they'll just tow the whole car off, remove the stereo, strip the car of anything else salable (engine, trans, wheels) and dump the rest on a back road somewhere.
Or more likely these days, get another $100 for the carcass at a scrap-metal dealer, few of whom are bothering to do the proper paperwork on hulk cars. And thanks to the demand for metals, the remains will be crushed and on their way to China in less than a week.
If they're just street thieves looking for something they can sell for that evening's dime bag, they'll just smash the window, pry the head out, grab anything loose that looks remotely valuable, and split.
Much as I'm a big fan of nice cars and flashy paint, the best defense is to drive an older beater, leave nothing in the car when you leave it (even piled fast-food wrappers and empty drink cups, anything that might make somebody think there's something hidden under there) and use an iPod or the like for your listening.
I've had to leave my rather expensive camera in the car a time or two, and that's worried me half to death each time. It's virtually always either covered or in a bag, but I still know it just takes seconds to bash a window, grab something, and leave.
And that pisses me off, because I tend to leave the camera behind thanks to that worry, and I've missed some interesting photographs because of it.
