We have a small yard for our two Swedish Duck, about 4x6-8 (never measured) so we wanted a small pond too. We ended up getting a 40 Gallon stock tank, positioning it closely to their house, and that leaves plenty of foraging room. We bucket it out with one of those 5 Gallon Home Depot buckets, get it done pretty fast and works well if you don't mind watering the yard! When we get to the end we fill it up a little more and keep dumping until it's clean water.
I guess buying a stock pond isn't really DIY, but for us it's the only real investment we have made in the duck yard- the house is made from salvaged cinder blocks and fencing with leftover lattice work. We acquired some stones from a coworker to create irrigation as no not flood/erode the yard when dumping water. I'll attach some pictures.
We buried the pond to the first rim, probably about 6 inches down and made a ramp up to it.