sounds pretty cool and very interesting, but you may want to check with your local township authorities and municipalities and anyone else you an think of- have a pond *right* beside a public sidewalk could pose a rather large danger for small children, so before you go digging or anything of the wort, I would contact people and make sure it is a legal idea.
Also, you might want to have people locate phone and hydro and gas lines under your house and make sure you can dig there! lol
I know this is pretty far ahead of your plans, but I just wanted to make sure that they were said
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