You're right you don't want to give Coolie any opportunity to get stuck. What about on the tank floor sort of under some
driftwood? that way it's not like Coolie
can't go there, he'll probably just have little interest in doing so once he sees that all that's different is the addition of a piece of zucchini (which I can't imagine him being very excited about). I found that the otos don't move around very much when they've got the veg to suck on (a soother??) so maybe then Coolie won't bug him, just sort of forget he's there. At least here's hoping??