Maybe give some thought to food prep and storage of these fish. A gill net will certainly do the trick, but may not be feasible if the goal is to harvest small amounts regularly.
If it were me, and it's not, I might consider a large harvest, and plan to store the finished/canned fish rather than try and keep them swimming long term. I don't know your goals, nor do I have an inkling of just what scenario you are preparing for. If it's doomsday, survival-at-all-costs, society is circling the drain, trumpets are sounding kind of thing, you're not going to want those fish swimming in a pond. You're going to need them smoked and dried, or sitting in a mason jar somewhere safe and protected.
You don't want to spend every waking moment watching your pond for leather-clad Mad Max wannabees, out looking for something to eat. Nor would I want to eat bluegills seasoned by a little fallout.
Course', if the scenario you have in mind is just for a few weeks duration, then that's different.
