We built a duck pond from a water trough. Phase 1 done. We have to finish other projects, but in phase 2 we will install the plumbing and pump to fill and drain/clean the pond when necessary.
Nice build! Part 2? I'd love to see how it turned out & how it works throughout a summer. If you haven't already, be sure the ducks can get out of the pond. Place blocks or something for them to step on to get out. Otherwise, they can drown. I learned the hard way.
Coming soon. I haven't figured out the way I want to do it just yet. Right now we just use a transfer pump to empty it out, a shop vacuum to get the stuff that doesn't get and its not bad. Will be working on it next month and making an update on it. Taking forever, but the ducks are the lowest priority for us. And yes, the water is kept full so they can always easily get in and out. I built a ramp and they never used it, so I took it out.
We live in the high desert, there's no toad/frog pressure up here. We see 2 a year and they're usually hiding in our irrigation enclosures. The pond is pumped out once a week with a sewage pump which has zero issue pumping it out and is much stronger than most pool pumps, especially for the price. You'd also have to build some sort of ramp for the ducks to get in, and then the frogs could go up it as well. We also freeze in the winter, an above ground pool would only be more susceptible and likely cause tears and damage. I'm not finished with the upgrades, but when I am I will add an update.
Impossible for you maybe, but we clean it out regularly and it's just a pump we switch on that goes to our orchard, with a deep clean once a month. People who have horses shovel manure, people who have dogs buy doggie bags, people who have cats have litter boxes... etc. Yes, they are messy, but so is every single animal on this farm.