I seem to remember there was a similar problem in WW1 with fighter aircraft shooting their own propellers off. Allegedly, the Germans solve the problem by synchronizing the machine guns with the engine rotation; the English solved it by putting metal reinforcement over the but of the propeller that was getting shot up.Does that help? Probably not. I suppose you could find out when the wiper passed the park position by reading the state of the park switch. Or by having a light sensor looking through the windscreen that detected when the blade passed over it.