I didn't he just doesn't do it.. lol
I find that most octos are content to stay where they are, I have never seen any of my octos try to escape. The most they do is reach out above the tank to grab my hands. Then after a little while of messing around they go back under the water.
I have lids on the top with maybe 3/4" gaps all around the lids (Arcylic tank) and if he really wanted to he could escape down the overflow (Flooding the house in the process) but again he's never been the slightest bit interested in getting out.
Eels have more of a habit of escaping than octos, and unlike octos eels can't get back in after they figure out it was a mistake to get out in the first place.