how much pond?

[v.cyr]

my GF an I have decided that our ducks are going to get a little pond when we build their pen, so I was wondering how big/deep I would have to make the pond for the 3(one pekin drake and 2 pekin hens) or 4(we might be getting a cayuga hen, too)ducks that we will keep?...also what sort of filtration set up would I be looking at?...

 

[TLWR]

A filtering option for a 10000 gallon koi pond for about a 50 gallon duck pond might do it....
Filtering for a duck pond is pretty difficult as well, they poop a lot and filters just aren't so great at that.

What I've found is that it helps keep the water circulating which keeps it from getting totally disgusting. My girls have been swimming in green water for months. We will drain, clean and refill in early May when the new ducklings arrive. Just so we can take pics of the new babies swimming LOL
My pond is ~900 gallons with a ~75 gallon skippy filter.