Thanks for the insights. That cutting the grass would be a huge cost did not occur to me but with enough red tape I see that could be the case.

Even though soil failure is the direct cause, if that fails the structure has failed. The reflex of adding more concrete does not always help. A hard, vertical structure is basically a concentrator for both currents and wave energy. So you need a huge scour protection or else the wall will only work very temporally. And a narrow structure is more susceptible to piping (where water finds a path under the structure and then erodes that away). This is of course also a soil failure, but unless you are building a boat you have to interface with the soil somewhere. And that is usually where your structure will fail...