The flood problem is one of the main reasons I am looking at the Bean Animal overflow. The thought of 1200 liters of water going inside the house while we are sleeping upstairs is not a pretty one. I'm glad your husband got away from thinking about the stresses of everyday life for a bit as well.
His ideas on the overflow are almost right but he is still thinking more along the line of Dursos. I also had problems getting my head around the principles as a restricted pipe running full siphon didn't make much sense. Then I thought about the times when I have had a snail in an outlet hose and realized that it didn't break the siphon, simply reduced the flow.
The full siphon is completely full of water all the time when things are working normally. That, along with a minimal flow in the Durso open channel, is what eliminates the noise. The beauty of the system is the added air hose on the open channel allowing for it to become a full siphon if the water level rises. Simple adjustments to the valve on the open channel set the water height in the overflow and then we just need to set the height of the air bleed on the open channel accordingly.
I originally thought about a toothed overflow but fish still seem to get over them and snails go anywhere they want anyway. Smooth weirs create less noise, especially with full radius on top. I have thought about going to a smooth slot but having them laser cut is pretty costly in Singapore, the nearest place I can get that sort of work done. I'm still considering making a box, complete with a thin base, out of acrylic and using the bulkheads to tie things together and then the slots could be easily cut here.
Another thing I am waiting on is information about the DC pumps now available. With electronic controllers they can be set to a lower flow and this might be good for redundancy as I could use two larger pumps at reduced flow rates and in the event of one failing the other could be opened up to pick up the slack. My only concern is that in the event of a power outage they may not turn back on at the previous setting with the electronic controllers.
The other way to go is use two large standard pumps with ball valves controlling the flow but then we get more heat output and use more electricity all the time. I may simply have to set things up so that one pump runs and have valves set for a spare one installed alongside to take its place in the event of a problem.
This is going to be a slow process due to ordering parts in from outside. Customs here can take ages.
If you want to see a good build for an Indonesian reef tank here (mostly in Indonesian but lots of pictures) take a look at My Dream Tank : 255 x 120 x 90 StarphireŽ Ultra Clear Glass | Indonesia's Saltwater Aquarium Hobbyist Community
The guy who did this really went all out with a large bank of batteries and inverter to take over during even extended power outages. Looking at the gear he bought was another reason I'm sticking with a planted tank. Local substrates are fine and once the glass, pumps, a few fittings like bulkheads and such, heatsinks, power supplies and LEDs get here the rest is just job work. That is until I decide to set up light controller but my wife has yet to approve that. Once she sees how much I spend on the rest she may never do so.