Originally Posted by TheMisplacedMidwestMom:
The 15 month old can open baby gates. All of them. 3 different types of closures. Walk through gates are no fun if you have to rig them closed. 
Teach them to never cross the boundary line....
I have walk through baby gates and/or half doors in every single door way of the house but I leave them all open all the time...not a single kid will cross the thresh hold until invited to do so....even my youngest (just over a yr old).
Here's a video explaining how to teach them boundaries
https://www.youtube.com/watch?v=wGa9BURyIw0&t=21s