I still say you can't fully prepare for hurricanes, tornadoes, earthquakes, ect. But the fish will need to be able to tolerate cold and hot temps. YOu can provide shade trees around the pond to significantly lower the temps in the summer. Also solar heating covers for during the winter to bring up the temps a lil during the day. Not much else you can do unless you plan to full insulate, and cover the pond so that it can be minimally heated during the winter. YOu'd be surprised how high you can get the temps with proper insulation. I like the half under/over idea. Will make viewing the fish really hard unless you have a platform to stand on with a locked gate so kids and animals can't get to it. You can net over it to keep predators out, but then you might ensnare a bald eagle and drown it or something. I know they are rare there but still any predatory bird. There are many issues to overcome with this kind of setup. I once had dreamed of doing a tropical indoor pond full of exotic catfish that people could pay to come snorkel with and possibly catch on rod and reel.
The massive building would have a natural pond right in the center and be very tropical climate with a dome and tropical trees from the amazon. Nifty idea, but I couldn't find any billionaires to bite lol.