We had an in ground light installed to illuminate our front step years ago. This summer I found the light fixture pushed out of place. I just put it back. The second time it was really knocked over and so we enlarged the area and added cement. Yesterday, a month later, the entire fixture, heavy cement and all was pushed out of place. The fixture itself is not damaged in the least. The ground is not disturbed except for this. We had removed pacasandra from this bed early in the summer and replaced it with vinca. I still remove a few pacasandra at times but did clean out the roots carefully. We see nothing and hear nothing. In fact the street light has always illuminated the house front. Does anyone have a clue as to what is going on?