Hanging lights from a gap?

I live in an apartment complex with a small-ish patio. Every year they have a decorating contest, and I always try to hang some lights using command hooks, but they never quite hold on to the concrete, so after a few days, I’m left with a mess.

Near the edge of the concrete, there’s a small gap – about an inch wide and about 3/8" deep. I was wondering if there’s some kind of expanding clamp (I have no idea what I’m searching for, so this is how I’ve been conceptualizing it) that I could put in the gap, tighten, and use that to hang lights from? I don’t know if such a product exists, or what it would be called, so google is failing me.

I’ve attached a picture of the gap.