I had this problem once with an eel that lived under a big piece of base rock. I built a second tank and left it in there. I'm sure it will be the longest lived eel in history.
I used a plastic cereal container with a lead sinker on the lid so it would fall closed. I had fishing line going to the sinker so I could hold the lid open till the right fish went in. Bait was a prawn (shrimp) tied to another sinker inside the container. I could have caught every one of my fish many times over. All except the one I wanted. Haha.