A Break Free Knot for Neck Carry
http://www.youtube.com/watch?v=864FSx_cTYQ

I really liked the idea of what was presented in the above video, but I didn't like the exact knot he used. Instead I use a nail knot and that seems to have enough tension for my tastes. A nail knot is similar to a hangman's noose and will come apart under tension - you decide how much tension.

Here's a link to the nail knot.
http://www.animatedknots.com/nailknot/index.php?Categ=fishing&LogoImage=LogoGrog.jpg

With this setup you can adjust the breakaway tension to your tastes and you don't have to glue anything or stitch anything.

The main thing I like about the nail knot is that it lays close to the skin. A lot of other knots stick out too far.