I can't really contribute much to this discussion, as I am not a tow pilot and my engineering skills are more in line with less complex functions, but with current technology, target tracking (as previously suggested) has become more available and reliable. Perhaps a laser tracker at the tow hitch and a reflector at the glider end of the tow rope could be used to trigger either a guillotine or release actuator. Parameters could be set so that normal "boxing the wake" maneuvers would be permitted and ignored, but a high tow angle relative to the tow plane longitudinal axis would trigger the rope cut or release actuation. Of course, this implies a sudden and dramatic increase in the vertical positions of the ends of the tow rope prior to upsetting the tow plane axis. A gradual "kiting" motion may pull the tow plane tail up at a rate that the angle does not exceed the preselected deviance angle.