I also live in the PNW and I partially bury my 100 gal tub to keep the water cool and stable in case we hit the 90's. Our temps swing quickly so try to keep your pond partially or totally shaded if you don't need the sun for plants.
It possible, do not have splashing water, like a water-fall...it attracts raccoons, herons, and other hunters of fish.
I have CPD also and like your idea of ponding them during our brief 6 or 7 weeks of summer.
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