Why not elevate the container slightly or set it on the ground and add a wick to help control the excess water retention resulting from a heavy soil? You can solve your problem by growing in a well aerated and less water retentive soil, too.

Al

I wonder if wood chips would work. I have them on my tipsy pots and the soil never washes out. I had been afraid that might happen, since they are slanted.

Do you mean a mulch of wood chips on top of the soil? Or do you mean wood chips as a component of your soil?

Thumbs-up to the former.

Thumbs-down to the latter.