Basically just 10% (even 5%) of the surface area of the pond needs to be ice free to stop a winterkill, and the diffuser should be in 1/4 to 1/3 the total pond depth, so putting one in front of your house should be no problem - depends on the HOA.
as for the gill net, again, just in front of your house would work. You take out trash fish and release any good fish. Talk to Karen and see about how she envisions the pond to be managed. Talk to the HOA board and get their blessing. Then once you have their blessings, you can tell Karen to go pound sand. A LOT depends on the HOA rules and regs.
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