I have always found the principle of self regulation to be one of the most interesting parts of the designer's manual.
I am sure that you are all familiar with the chicken diagram
http://portlandmainepermaculture.files.wordpress.com/2008/03/permaculture_chicken.jpg I had a try at this myself and did something similar for dogs.
I wondered if anybody else had done a similar exercise with other species, or perhaps could spot any glaring mistakes on my attempt.
Chris