Hello, I'm new to Yorkie Talk. I put my little 13 week old female (CoCo) on the Second Nature dog litter system the moment I brought her home when she was 8 weeks old. She has been very reliable considering her age. I have been keeping track on her "accidents" and right now it's about one accident every other day. I've spent a lot of time making sure my potty training efforts were consistant. I think I got lucky with CoCo, she picked it up rather quickly. My Dachshund is about a year old now and is no where as consistant as CoCo. Be patient and don't give up! Stay consistant and make sure you learn when Chachi has to go potty. I learned CoCo usually goes after she wakes up from a nap and after she eats so I used that to my advantage by putting her in the litterbox during those times.
Here's a video I took of CoCo going to the litter box after waking up in the morning. In this video she's 10 weeks old. I feel weird showing a video of her going potty but I figure it will keep you motivated potty training Chachi.
http://nyip.net/~iarciaga/coco-litterbox.wmv