For a chicken coop me thinks this is being overthought a bit here. Dig holes-place posts- pour dry sackkrete and add a bit more water. Stand back and wait about an hour and try to get that post out of the ground.
+1
I got to thinking maybe an hour is a little fast so I ediited it to a few hours. But still, an hour, two hours, three what the hell! You'll play hell getting that post out of the ground.