I have a concrete mixing pan and recently a friend gave the ducks a 4' diameter kiddie pool her pups had snubbed.
Regarding a water feature type pond, that sounds gorgeous! I would consider that, as long as I could figure out ahead of time how to handle the sludge. Poop is relatively minor compared to the vegetation that my ducks like to bring to the kiddie pool to play with.
When I used to design livestock watering systems (basic stuff, not rocket science), we always used 4" Schedule 40, because it is durable and widely available (at least where I was), and most things like leaves and such would flow through without getting clogged.
Some things that you might be able to use might be a wire cage around the outflow, 4" pipe, a T- or Y- cleanout for when it does get plugged up.
Many pond fountains use pumps with 1" or 2" hoses. In that case you might want to have some kind of reservoir where stuff settles or floats, and set the small diameter pipe in the middle to reduce blockage.
Those are my thoughts - enjoy the ducks! Take advantage of the BYC search - we have discussed all manner of topics.