Succulents on the Half- Shell

Spring is planting time and I've been searching for small succulents to plant in this shell planter I found at a great estate sale last fall.  I found some at Home Depot and finally got this project done.

I used some white spray paint to give the shell a brighter, cleaner look.  Because there are no drainage holes in the planter, I put a layer of charcoal in the bottom so it doesn't end  up smelling like a swamp!   Next, a layer of small pebbles for drainage and then filled it with cactus soil.   After plopping in my little plants, I sprinkled some aquarium gravel to finish it off.

 Once the weather gets warmer  the shell will head outside for some real sun.  I'm wondering how the no-drainage thing will work when we get some serious rain.