I took this shot of the ha-ha wall whilst walking at Croft castle this afternoon..... ha-ha is a ditch with a wall on it;s inner side below ground level ,forming a boundary to a park or garden with out interrupting the view.
I agree with @judithdeacon - great composition. I do like a nice ha-ha - whenever we go past the one at Wimpole we always say 'look, funny' in a pathetic family joke!!