I actually had this same stair issue with my lab when I first got him. He was about three years old at the time, and he was terrified of going down a flight of stairs. When I brought him home, he crept up the stairs, but in the morning he didn't want to come down. It took my sister and me three days to teach him how to go down stairs. The first day I took his rear end, she took his front end, and we carried him downstairs. The second day I put him half way accross my lap, and we scooted down the stairs. Then on the final day, I blocked my dog's exit at the top of the stairs and kept moving down behind him; he had no other choice but to walk himself downstairs. After that, I never had another problem with his fear of staircases. I probably could have acheived the third day's result on the first day if I'd figured out that blocking his retreat forced him to overcome his fear.