Anti burglar plants for a wall

[Ihatenicknames]

My house shares a boundary wall with an alleyway. My side of the boundary wall has no soil (just a v narrow side passage) and I want to grow something to deter burglars. I was thinking of using window boxes on the top of the wall and planting something prickly and trailing in them but have no idea what. Any thoughts? Thanks

Generally plants would need watering and you'd have to fix the boxes to the top of the wall (otherwise they could just get pushed off). What about cacti as they don't need much watering and would certainly be a deterrent if the boxes can't be pushed off!

How high is the wall?

I think you'd be best off contacting your local police for advice on how to make your wall less appealing.

The wall is about 7 feet high.

We've planted some pyracantha in front of our fence - grows quick, is pretty, has thorns. We've since discovered it also causes extreme itchiness when touched!

Pyracantha is a very good deterrent. I grew up in a house with a similar lane running down the side. The previous owner had cemented broken glass into the top of the wall. It was useless as the would be burglars would just put a coat over it to gain access.

Hawthorn

Cockburnianus has viscious thorns and spreads by runners. You would need deep screws into your wall to kee the planter secure. I would screw some tall trellis to fence, like mine.

Vicious of course, oops