I skimmed through this, but I highly highly discourage yelling and spanking. Like Karen said, especially to dogs like Terriers, your yelling and spanking is totally working against you. It provides the dog negative attention, and, honestly, the dog does NOT understand why it is being punished unless you perform it WHILE the dog is peeing. If you spank or yell anytime after, you're teaching the dog nothing.

Please look into some structured obedience classes. The trainers go through these issues all the time and they'll be able to give you some insightful, personal training and advice. It will also help build your dog's trust in you and you guys will have a better overall relationship.