We had been putting off getting a baby gate to block of the stairs. He didn't really seem to be all that interested in the stairs until this week. We needed one that was extra large, since the opening to the stairs is quite wide. Thankfully, our friends, who have just about any baby item you could want, let us borrow a baby gate they had, and it works great!
So, no more stair climbing for a little while, unless Mom or Dad lets him.