Summer (brand) Infant Wood Top of Stairs Gate (would work for pets too!)
This was an awesome gate! We bought it because I needed one at the top of stairs at grandparents' house, yet they absolutely did not want me to put holes in their walls or bannister. This gate was the only one I could find that could be installed without having to put holes in their bannister or walls. I found it tonight online for anywhere from $90 to $160. Selling for $45. You are welcome to come and look and see if it's what you need before purchasing.