If the waves arriving at the coast have a 10 second period, coastal retreat rate is 20 cm/yr, and the horizontal exponential length scale for decay of flex-swaying of the cliffs by the load of the waves is 15 m, how many wave cycles will a rock mass experience significant strain before the cliff wears back to it. Here we define “significant” strain associated with the swaying when the amplitude is 10% of that at the cliff.