OK, so here's my plan
I have a large "hard" plastic pond liner that I'm going to be installing a sink drain in that runs out to 1.5" PVC pipe and a 1.5" ball valve. The pond will be buried into the slight slope in the pen, and I'll surround it with either tumbled concrete pavers and natural stones, or just all natural stones, to cut down on the dirt/gravel/grass/detritus that seems to migrate into duck ponds (based on my understanding).
Long term, I'm going to turn it into a smallish aquaponics (duckponix) setup where I'll have a similarly sized pond liner/rubbermaid trough buried in the ground outside the enclosure and connected to the drain system with a T and another ball valve (so the pond and the trough/pump enclosure can be drained separately). The duck pond and the trough will be level with each other, so if we do not have power or I decide to take the pump offline, there will be no problems with overflowing. The trough will have a false bottom a few inches up, to allow for sludge accumulation (I'll probably use the egg-crate stuff they use for fluorescent light grilles), then sit the pump at the end of the trough farthest from the input/connection to the duck pond. The line from the pump will connect to the bottom of one of the large $18 fiberglass planters they sell at costco, which will be in the duck enclosure, but not buried. I'll drill a hole in it towards the top to drain back into the pond.
The costco planter will have water lettuce or water hyacinth floating in it, and be filled with furnace filter material.
The trough will probably have a secondary false bottom (towards the top) that I can set basket pots of stuff like pumpkins or something in to take advantage of the rich nutrient content of the water. I may also grow kale or greens for the ducks here?
The benefit of having the secondary tub is to keep the pump out of the duck pond, which should theoretically help some of the weirder solids like rocks and feathers settle out prior to hitting the pump, hopefully extending it's life. It also gives me the option grow stuff without fighting the ducks for it.
The 2 ball valves (one on either side of the "T") allow me to drain/service/manage the pond/trough independently.
Here's my sketch of the idea.
The only other thing that I can think of that would probably be useful, is a few weeks ago, I saw something where someone used a milk crate as a pond pump prefilter by lining it with furnace filter material and making a swinging "lid" out of wire mesh fencing material. I don't know if this would be prone to clogging or what, but it may be a decent option if I find pumps are getting chewed up by solids.