Independence vs. Safety

As parents, how do you draw the line between keeping your kids safe versus nurturing their independence?

I thought I had it all figured out. At the playground, I have evolved from the over-protective mother hovering over my children at each stop on the playground to the relaxed mom who can see and react to her children while keeping an eye on all three no matter where they be. I no longer felt like I had to be on top of them. I've finally allowed them to quietly play soccer in the middle of the track where I walk every morning. At home, I've slowly started to let Einey and Meenie play outside on the deck alone and even more recently, down in the fenced in (but not completely gated) yard by themselves. At three and four, they've earned that independence. Now don't get me wrong, while they are technically outside by themselves, I am usually within sight of them and if not, I am peeking outside every few minutes to check on them. We live on a main road but the yard is away from the road. Their are no sidewalks or places for people to be walking by.

But earlier this week, less than a 1/2 mile from my house (closer if you make a direct line, there was an attempted kidnapping of a 6-year old little boy. This happened in the early evening, just before dinner time, while people were outside around the child. The area it happened in was an area with lots of sidewalks and houses. A place where kids freely roam. A place where there is always someone watching. Here is another article related to the attempted kidnapping.

So I ask again, how do we keep our kids safe? I don't want to hover. I want them to gain independence. I already scan the faces of the other playground patrons to see who is with who and if their are any "strange" (which is completely irrelevant as most people who live in this area would fall into that category) people hanging around. I try not to go to the most popular playground except in the "off-season" so as the avoid the crowds.