My suspiscion is that the verge is considered part of the road and therefore belongs to the council and you cannot put rocks on it – but I may be wrong.
Years ago I was going down a country road and huge tractor appeared around the corner I was approaching and forced me to go onto the verge which had been decorated with rocks.
That cost me about £400 for two new tyres and a new alloy wheel for my Volvo V70
If I’d known about the verge ownership thing then I’d have taken him to court
I remember my brother done a similar thing. In my dad’s brand new company car 8O.