Well lets back up. Octos are predators, and therefore anything in your reef is food. So, if you want a reef tank to slowly be depopulated, introduce an octo. They are escape artists and I actually have video of an octo climbing up the glass, going over the side and into the tank next to him to eat shrimp. They will go through J Tubes to get to your refugium etc.
They also rearrange the live rock at will. We have a large octo rearrnage his rock every other day, moving stuff around looking for food. They are deceptively strong as well.
That said, IF you don't want to lose a lot of $$ on feeding him, I'd put him in a species only, self contained tank with disposable live rock.