Potty training a 5 year old dog?

I have a shih tzu about 5 years old and I love him alot. I take full responsibility for not properly training him in the past. I have been clicker training and have been training more often and he is great! I feel bad that I hadn't made an effort like this in the past but now that I am ready to fully train him I was hoping to get tips on how to break him of his bad habits. He tends to pee in the same spot behind a big leather chair on the carpet. He goes potty inside pretty often and I'm ready for him to start going outside. We have used a cleaner on the spot where he goes and I have had a little closer eye on him. So far so good...but tips on how I can get him to go outside would be helpful :) I like the idea of teaching him to ring a bell to warn me but I don't have one and I would rather something like barking maybe but something along those lines for a warning. If you have any tips or any ideas on ways he can tell me he has to go out I would appreciate it :)