Build Your Own Baby Gate. This is great for the bottom of the stairs, or the top, if you used a more child-proof latch design. Maybe just putting the latch on the side the kids aren't supposed to be on would keep little fingers from opening this. I REALLY love how it looks--and it's really just a half door. Perfect.
Need to install a baby gate, but don't want to drill into the wooden stair banisters??? Cut a couple of 2x4's to the height of the banister, paint,and secure with heavy zip ties. Then just add the baby gate hardware to the new piece of wood........D.