[bamfly]

I'm quite sure he means a post-hole digger. I can practically smell the odor of digging in rocky soil with those, coming off the page, almost feel the cracked dust-sweat-caked knuckles of setting posts on a hot, dry day.

[EDIT] As for the rest, putting aside metaphorical readings, the clockwork-like progression and repeated crossing of the line of holes calls to mind the stop-and-start movement of running barbed wire and working a ratcheting tensioner tool behind the one digging the holes, and in the right country, the curious among those workers may pause to reflect on the remains of long-dead things (fossils, "bones"—fish, horse, bison, mammoth, spine-like crinoid stems, shells and coral from an eons-dead sea, even dinosaurs—the ranches and farms of the West largely sit atop the shallow graves of life's history on Earth) sitting flat in the dirt or exposed by the digging, while others may pay them no mind. There's definitely a defensible reading of this as on the surface a plain, if oblique, description of a work crew running a fence line—not just the one digging the holes, but the whole set of folks described. I'd wager that's what's intended (though not the only thing intended), in fact.