Most thieves are not looking around wildly when they are doing their deed, are they? (you've all seen surveillance camera footage)

When DH cut through a cable we had in public, we noticed that people didn't look at what he was doing. It was kind of dark, but i'm sure if he was stealing he would have gotten away with it. Now that's not to say that SOME people
will confront suspicious people, whether or not it's dangerous. But counting on those folks to be there...

So what CAN we use to keep our bikes from getting stolen?