I'm not sure how long you've owned ducks/geese, but know that they foul water QUICKLY! (ducks moreso, in my limited experience with geese... sometimes my goose takes a thirty minute dip in the tub and won't poo once in there, yet my ducks go as soon as those fluffy butts hit the water)
Even back when I just had three little Mallards, they could turn their newly filled 600 gallon stock tank putrid green in less than three days. My mind was blown.
So whatever you make, learn from my mistake: make it VERY easy to clean.
Some people have had some success with filters/waterfalls and other things I've no experience with, but even those have to be cleaned very often, as feathers and other stuff will clog them up.
Me, if I could go back in time I just would've gotten a couple of kiddie pools. Easy to dump, easy to fill. Emptying and refilling that stock tank is an all-day process, and even though I do it every Sunday it's still disgusting!