Years ago I was involved with a facilty where we had a 7' Black Mamba in an aquarium tank w/secure lid. We kept a hide box with a drop door controlled by 2 strings from the top. The door was weighted, and the box was grooved so the snake couldn't push it open. Most of the time we just kept an eye on the snake and lowered the door when the cage needed cleaning and it was in the box. I did enjoy watching Rom Whittaker's King Cobra video at Daytona where he uses a large bag and a pvc pipe at one end when catching them in the wild. Seemed to work well.