I recently noticed an old brick wall crudely topped with cement in which there were embedded shards of broken glass. The glass had all been levelled off and made comparatively safe, but it reminded me that this was once a cheap line of defence against intruders.
I sauntered on the road back to Barkingham for about five minutes, then struck off sharp for the plantation, lighted my lantern with the help of my cigar and a brimstone match of that barbarous period, shut down the slide again, and made for the garden wall.
It was formidably high, and garnished horribly with broken bottles; but it was also old, and when I came to pick at the mortar with my screw-driver, I found it reasonably rotten with age and damp.
Wilkie Collins - A Rogue's Life
Of course a determined intruder could just smash the bottle shards level with the mortar or just break up the mortar as in Wilkie Collins’ novel, but why don’t we see such things any more? Is it too dangerous to the intruder or just ineffective?
My guess is that the owner could be sued and that’s enough to get rid of it. Plus the possibility of horrendous injury to a thoughtless child. As a child I knew what the score was with brick walls, but I still wouldn't have one on my boundary. Horrible idea.