Buddy afraid of stairs

Buddy (7 years old) recently became afraid to come down the stairs (wood with rubber treads). We live in a split level and he has no trouble going up, as the bedrooms are up, and he wants to sleep with us. But recently panics about coming down. (I've been fencing off the stairs and sleeping on the main floor with him in the living room.) He also has no trouble going up or down the stairs to the basement (carpeted with anti-slip treads) or the concrete stairs out to the back yard.
He has had this problem before, and we have retrained him to calmly walk up and down them. I do believe that he may have had a scare or two when we weren't home, (after hearing the mailman at the door etc., and running down the stairs).
My question is this:
What should we put on the stairs so that he won't slip and will feel secure, even if he's in a hurry??
Any ideas?
Thanks,
Pam & Tom