HELP!

Okay ladies, I'm in some serious need of advice... my son has started a horrible habit (well several actually, but I'm not going to talk about stripping in this post):

He thinks it's funny to run away from me in the store and hide.

His mom DOES NOT think it's funny.

Now I know what you might be thinking: just keep him in the cart. And I do, when I'm somewhere that has a cart. But what do you do when it's a store that has no cart like the mall (and my son will not stay in a stroller) or when you go into the dressing room and he climbs out under the door when you're standing there in your underwear?

That happened to me in DI this week. I'd already pulled his little hiney back into the dressing room four times as he tried to escape but he was too quick the fifth time. I hurried and finished getting dressed and then opened the door to see where Kaleb had gone. I couldn't see him ANYWHERE. I called out his name and he didn't come. Panic immediately set in as I'm looking around calling out his name, just visioning that someone has kidnapped my child. After what felt like an eternity, I found him. I turned around and he was just standing there, looking at me like, "What's the big deal, Mom?" I chewed him out for running away and he just kept saying, "Funny." (his favorite word right now. In fact he's saying it right now) And I just kept saying, "Not funny. That was NOT funny."

HELP! What do I do? He's done it multiple times now and he always laughs and says, "funny." I've spanked him and chewed him out, but what else can I do besides putting him on a leash or never going shopping again?