I recently put in a small number of tee posts around the vegetable garden (wife's idea to keep the deer out).
I used a 5 foot pinch bar to make a hole. Maybe four or five "plunges" went as deep as required. Stepping on the plate to get it into the dry ground (sturdy shoe soles) and a few hits with a 3 pound hammer and all was well..
We have way to much stone here in Vermont. about half the holes hit something less than a foot down that reqired a two handled post hole digger to ferret out. One location, after a couple of strikes with the point, had the bar go down 3 and 1/2 feet . Must have been a rotted tree stump or the like. I'll remember to keep equipment off there! ;-)