I got this idea from Huarache Blog here: http://huaracheblog.wordpress.com/2011/10/07/museo-nacional-de-historia-mexico-city/
It's basically a triangle in front and a strip in back. Holds the lacing in place.
My piss-poor implementation using scrap leather that's just too thin actually works pretty well. This really enhances the comfort of the huaraches and I think if I did it over again with better leather, it would look pretty good, too.
The front: http://farm8.staticflickr.com/7153/6846633309_8c5e6d62f3.jpg
The back (upside-down and blurry, sorry, ipod) http://farm8.staticflickr.com/7199/6846633663_914bfdf3c4.jpg
