A number of different mechanisms are used for releasing the
V-bridle on a two or three point aerotow system. Two of them are pictured here.

http://estore.hanglide.com/Aerotow_Primary_Release_p/14-9004.htm

http://ozreport.com/16.019#1

Mark Dowsett has been here with his students and he uses Joe's "Get Off"
release. The duct tape and zip ties have been replace with Velcro. The Monkey
fist with a large washer. The point of his release is that there is a consistent
small amount of force (due to the spring) required to release the V-bridle,
irrespective of the pressure from the V-bridle.

http://www.nanoavionic.com/