Are you using winter blades with the rubber covering , and does this happen mostly at highway speeds ?
If so , it's the airflow pushing them off the glass .
One thing to try is a shorter blade and/or summer wipers .
Next , being carefull , is to pull the arm away from the glass , and slightly bend it in the middle as if you're moving the blade closer to the windshield. This will put a little more tension on the arm spring.
Now go buy some rain-x . And use only rain-x washer fluid. The cheap blue stuff just removes the rain-x so you have to re-apply every two weeks.
Archimedes screwed us !
I knew a blonde dyslexic agnostic insomniac - she'd lay awake at night, wondering if there really was a Dog.
2003 Ranger Edge 3.0 manual 2WD