When I 1st got my yorkie, some 17 years ago, I kept Picasso in a small carrier during the day when I was at work. I would come home at lunch, take him out, and put him back in until I came home. THis worked for me, as I assumed he got tired of being in the poop and pee, so he learned. Of course, he did slip every so often, normal for a child I guess. Give it time, I am sure it will work and try those pee pads, they are helpful, because they absorb.
Cheers from NC ~ Mark
RIP Picasso, I love you!