How about mounting a camera on the towplane that's keeping an eye on the glider. If the vertical position exceeds some predefined rate of change, the release is pulled.

Got this idea from this story:
http://www.gizmag.com/air-hockey-tab...r-parts/30840/

A camera is mounted above an air hockey table and software is able to track the puck and use that information to drive a paddle to return pretty much all incoming shots.

To test this out one only needs to mount a camera on a busy towplane to collect lots of "normal" operations as well as some simulated kiting scenarios.. Then some smart person could analyze the video to see if it's possible write some code to effectively track the glider.

The big question is whether a kite is detectable early enough, and different from normal operations.

-Tom