I had this little 3" wild caught Oscar that was easily the most beautiful Oscar I had ever owned....but man was he mean....even a 3". So I made this black acrylic box with a clear front about the size of a 5gal tank and drilled (and it took hours) tons of holes in it. Then, I put a little recirc pump down in the bottom and placed the whole thing in the tank. When the Oscar would start punking ALL the fish....and they were all big than him by quite a bit, I would catch him and put him in the little "time out" "penalty box".
I was sad because he would pout...like Oscars do....he could see all the fish swimming around....
When he terrorized all the fish, they would all hudle together on one side of the tank...but when he went into The Box they would all come up to see him in there. He would of course try and attack them through the clear acrylic.....when he stopped trying to get the fish that would mockingly hang out right in front of him, thenni would let him back into the main tank...took a couple days. He would be good for two or three days then he would wind up back in time out.
Anyway, obviously I couldn't keep him anymore so I gave him away...but the little time out box bought me some time to find a good home....