I did the sort of the same thing for Taycie. When I first brought her home I was using puppy pads, it worked fine at home but at work she would go outside like the other dogs and well long story short she started to become really confused..
So my alternative was a sod box. I got a piece of sod and planted it in a long shallow under the bed box. I also drilled holes in the bottom of the box for drainage. And then I chucked the puppy pads out the window.
Honestly, was the best invention yet! I use my sod box when I am out long and just pop it in her xpen. Solved my potty training issues almost instantly! ... Yes! I love sod... we are not crazy yorkie moms just smart
