"There's a whole hobby out there of collecting photos of stone gateposts with rectangular holes - bet know one has even thought about it ;)"

Let's face it, a whole culture of standing stones must have been uprooted and is now holding up gates, unrecognised. If your gatepost rots and there's one convenient to hand, well you would, wouldn't you?

And how do you ever find the truth of this -
"Survey work between 2002 and 2004 by the Strumble-Preseli Ancient Communities and Environment Study (SPACES) recorded an enclosure on the upper part of the outcrop consisting of a steep-sided promontory with a bank of stones across its neck. Although only around 3,500 square metres in area the enclosure contains several dolerite outcrops, each naturally fractured into shapes that could be formed into columns. Semi-worked megaliths lay scattered around apparently having been simply levered out from the larger outcrops. It is debatable whether these "semi-worked megaliths" are prehistoric or recent, since this area has been used by the farming community for at least 300 years for the collection of stone gateposts, lintels and building slabs."