Hi saw you're dog was having the same problem as mine have had, I found that chicken gave both of mine the runs.
They both had bouts of the runs for several weeks, I even had the vet test their poo at a cost of £70+ and the tests came back clear.
I then purchased a breed specific diet book from Mr Cusick and the change was instant, no more runs and really healthy looking coats.
The book cost me $30, which is about £16 and took 4 days to arrive; the recipes were very easy to follow and didn't cost the earth either.
http://home.att.net/~wdcusick/free.html
hope this helps