A block of ice the same length and width as the as the plinth, and ten foot high. Replaced when melted for a year.
The tracking sun warming the southern, Nelson-facing elevation would sculpt the ice into a blade of sorts, and create a slow waterfall. People could use mirrors to burn holes in the back. And the pigeons would be totally bemused. It would also serve as a representation of time - a temeperature clock for the people passing it each day on their way to work.
A natural winner. I hereby claim all intellectual rights.
