First things first, we got a new puppy!! Here she is..
She's an Irish Setter, and we figured out pretty quickly that a regular plastic tension supported gate just wasn't going to do. So, I found this GREAT online tutorial and promptly gave it to Dusty. http://www.remodelaholic.com/2012/09/diy-barn-door-baby-for-stairs/
We built it out of Pine, which is on the expensive side but it probably the sturdiest lighter weight wood. Read the tutorial for specific instructions but basically you build a square to the measurements you need your gate to be, then attach trimmed boards to that frame. The "X" detail is probably the hardest part, but its purely aesthetic so can be skipped if you don't have it in you.
The finish turned out great but I will warn that this is an oil-based paint, so don't use it unless you have space you can dry your project in. Its VERY fumey.
We framed the wall and mounted using SUPER heavy duty bolts and a self closing hinge.
Here's another of the finished product: