I just read about the M-Edge Guardian Case on Wired:
http://www.wired.com/reviews/product/pr_medge_guardian
+ Waterproof and Durable!
If M-Edge makes one for the Kobo, I think it would be an excellent protective case!
http://www.medgestore.com/
Just emailed to ask if they've any plans on developing one for Kobo EReader.
Peace and God bless.