Towpath bridge parapets covered with corrugated steel near the Aston Locks
Coming up the Birmingham and Fazeley Canal in the heat of last Saturday, between Salford Junction and Aston Junction there are many former arms. Those which lead off the towpath side have bridges over the main line's towpath. The parapet nearer the canal is the conventional brick design leading up from the ground such that it wouldn't snag a towrope. But the other parapet has, in most cases, been covered with horrible corrugated steel coated with anti-climb paint.
Presumably these parapets were too easy to scale for those intent on breaking in to canalside properties. I can't think of any other reason for doing it.