Thought this was pretty cool, since I've worked on some bat-friendly cave gates in the past. Check out the site, below, and view the students making the gate and what it entailed.
Ernie Coffman
Participants in the workshop learned how to build bat-friendly gates to make abandoned mines safer -- while still allowing access to bats. Twenty students took part in the weeklong workshop.
http://www.blm.gov/ca/news/newsbytes/xtra-06/234-xtra_batgate.html