Potty training.

I acquired my Bichon when he was about a year old. He pees all over the house and I can never catch him doing it. He goes out about 6 times a day so it’s not like he doesn’t go out enough.
We always goes potty outside but if I am gone from the house I can be sure to find some little piddles. How can I stop this? I have a lab also and he isn’t a problem.