Power and Polarity protection circuit layouts

[mr.adambeck]

So in building pedals for myself and one as a favor for a friend, I've magically ended up with two people who want to PAY me to make them pedals!   While I trust myself to only use nine volt power supplies with the correct positive/negative orientation, I don't trust the people I'm making these for (well, mostly just one of them  ).

From doing a search on here, I've found a couple geofex links on polarity protection:

http://geofex.com/Article_Folders/mosswitch/mosswitch.htm
http://geofex.com/Article_Folders/cheapgoodprot.htm

But am wondering what else is out there, and especially if there are any well drawn layouts (I'm still relatively new to all this and don't always have the best time working from schematics as opposed to layouts).  I essentially would like to make these idiot proof so that there's no way they could fry anything.

Thanks!