Free Plans 2D and 3D, for obtaining a quote from any laser-cutting service. More expensive than a quality post-driver, but very much easier to employ.
Slide Weight Half: Make 4, 6, or 8 of these. PDF SLDDRW SLDPRT
Slide Weight Handle: Make only 2 of these. PDF SLDDRW SLDPRT
Assembly: Build like so. PDF SLDDRW
The driving action is as easy as lift and drop. Never does it fail to strike perfectly squarely. You can add or reduce weight simply by assembling it from more or fewer non-handle sections.
A ham radio friend of mine fixes a water hose to the tops of 10-foot long, ¾-inch copper pipes which he uses as ground rods, one each for his several antennas. With water under pressure as continuous lubricant. Although being 70-plus years of age, he easily works these pipes all the way in with no tools at all.
Because of fitting around the pipe, my custom driver leaves the top available for similarly supplying continuous lubrication. Under pressure for driving a well point. At a trickle instead for mudifying deep-down soil so as to up-fill an open-end pipe. I look forward to trying this latter come spring at my next antenna-mast raising.
A medium length of galvanized pipe driven into the earth* can serve as the base of a tilt-over ham radio mast or tower. Driven in at an angle, a guy anchor. Unlike poured concrete, abandonment would only require driving the end below surface level. Do fill in the pipe rather than leave it hollow. Else it may short-circuit the filtering of soil above the water table.