Suggestions, anyone?

I'm at my wits end.

My son has decided it's funny to run away from me. In the store. In the parking lot. Into the middle of the street. It often happens when I am preoccupied with his sister. All it takes is one split-second of diverted attention and he's off. He's a fast little sucker too.

I've tried everything: yelling, time-out, take toys away, take his lovie away, and even resulted to a quick swat on the rear in particularly dangerous situations (no, I do not spank my children as a general rule). Nothing works. It's often hard to do anything about it since it happens 90% of the time with his little sister. I can only do so much when I'm holding another baby in my arms.

He loves to run, he loves to be chased, and he really truly thinks it's a game. I have no idea how I'm supposed to reason with a two year old.

And so I'm coming to you, our readers. Any suggestions? Anyone experience the same thing? I'm desperate.