The first being to simply dive down and grab the octopus with your hand, out of whatever rock crevice it’s hiding it. A blunt rod can help in this by coaxing them out of their hiding spot.
The other way is to use a sharpened spear or knife and attempt to impale the octopus while underwater.
Lastly, certain commercial fishing traps or more traditional earthenware clay pots may be used as a more hands-off alternative.
The Fitbit Rabbit chose the olde hands-on approach when an Octopus he did so bravely pouch!