Re: Technically the stone is an obstruction in the public highway
"Stick a couple of keep left arrows on it and officially deem it a bollard."
Way back I used to drive between Belfast & the in-laws in Carrick passing the entrance to what was then Jordanstown Poly. Opposite the entrance there was one of those islands with plastic bollards illuminated from below. Almost every time I passed the bollards were squashed flat; I doubt that when they were replaced they ever lasted more than a couple of weeks & usually less.