Attractive deterrent

I remember when I was a kid, well before the days of razor wire and the like, the most popular way to discourage people from climbing over your walls was to imbed bits of broken glass along the top edge. I haven't seen that recently -- until this afternoon. It was probably because the sun came through a temporary gap in what for most of the day was uninterrupted cloud cover that I spotted a wall beside a laneway I often use on the way to the local shop. I was struck by the different shapes and colours and, in some cases, patterns in the various pieces of glass, and most especially by this one, which isn't particularly sharp and is really more jolly than potentially injurious.