So that means its not going to happen in the future?
I've got no idea what the wood looks like, but clowns are notorious for getting stuck in "nooks and crannies", maybe they haven't yet but as they grow the gaps will become tighter and the chances of a fish getting stuck increase. It happened to me, I had an awesome hollow log about 3' long with various holes in/out of it, was a fantastic hiding place for 10 small clowns, but a couple of years later they were getting badly scratched from wedging in there so tightly. Eventually it got to the point where the first one in couldn't get out unless the ones behind it backed out, so I had to remove the log. Wasn't easy shaking them all out of there, they squeeze in pretty tight!
I'd suggest using some flat pieces of schist to make some caves they can't get stuck in, or PVC pipes if you don't mind how they look.