Help me stop the windshield wipers coming on at 80mph

Update:

so first let me just say there is one place on the car that I detest working on, and that is under the dash. No surprise then when I have my wife actual the wipers by hand that the shaft is rotating around the spindle and two quick half turns on that nut pretty much stopped the problem.
However, I have these old "Rainex" wipers with a single fin standing straight out from the entire length of the blade about 3/4" and I recently changed the stance of the car. I have convinced myself that combination was not helping. Add to that the fact that the aforementioned ANCO wipers with the aero wings, in stainless, are better looking.- I bought a set of them anyway! These cost about as much as a remanufactured 2 speed wiper motor for anyone else finding themselves in this particular rabbit hole.
So weigh your options wisely..... but do try the nut first!!! lol