It sounds like this dog has IBD or irritable bowel disease. Thickened intestinal walls, chronic diarrhea. weight loss, inability to absorb nutrients. Did the vet initially diagnose IBD, if not, what did the vet say the chronic diarrhea was caused by? When dogs are put on a raw food, grain free , corn-free diet, the symptoms of IBD decrease and the inflamed intestinal walls should start to decrease in thickness. Corn is in alot of pet foods. Peppermint, alfalfa, slippery elm powder , digestive enzymes, increased protein, increased fibre such as psyllium , anti inflammatories can help. Even if the dog does not have IBD, the symptoms are the same so if you read up on IBD some of the things listed to give for IBD may also help .

http://www.gcvs.com/internists/ibd.htm

http://www.insecthobbyist.com/articles/IBDChat.html

http://www.peteducation.com/article....articleid=3418

http://shafferah.com/ibd.htm

http://groups.yahoo.com/group/IBDogs/