Wreck-Diving.org

In Hawaii, when we dive to spear octopus, we go during low tides. Usually the octopus are in there "homes" during low tides and hunt for food during higher tides. Octopi live in holes in rocky, not coral reef, shallow areas (I did notice you said deep sea). Because they feed on crabs and shell fish, you can usually find their homes in similar areas that you would find crabs, lobsters, etc. The holes usually have multiple entrances and is usually found in flat rocky areas. A typical hole at which an octopus resides in have a lot of small rocks, shells and debris around the main opening. A lot of times the debris will have discarded and crushed shells from past meals.
It takes a while to recognize what these homes look like. Often times you won’t be able to see the octopus when you look in the hole because they blend in so well and the octopus are extremely intelligent creatures. Keep looking and you will eventually get the "eye".

Have you been looking for them at night? On a typical night dive, I would say the chances are pretty good to see an octopus if you are moving slowly and not waving your light around like a madman.

Night dive, keep to the bottom

The sea is pretty big and there’s a lot of hiding places for an octopus. Don’t worry about it, keep your eyes open, look at everything and take an interest in your surroundings when you’re down there and the octopus will pop out when you least expect him to. Other than that, do night dives and check all nooks and crannies. They’re pretty crafty at hiding themselves. (Don’t stick your hands into any holes – you’ll get a nasty surprise, that’s for sure – especially at night:-) I’ve done about 1100 dives and still haven’t seen a single seahorse – and I’m looking real hard.

My dad saw an octopus the first time he took a LESSON diving. Just let them come to you. They’re really cool.