First thing of course is to stop shouting at himl as shouting could have preceded awful, fearful things in his past. His piddling is from anxiety, stress and fear most likely. Until he's better at the stress peeing, avoid looking directly at him or greeting him when you first get home or anytime you enter the room he's in and don't acknowledge him at all until he approaches you. That will help him avoid what he sees as "confrontation" and tend to lessen his anxieties. You might try tossing treats ahead of you as you come into his presence - something to show him you mean him no harm and it won't mean direct confrontation as he'll be busy going after the treat or piece of kibble.
You have no idea what he went through so imagine the worst and treat him as if you are rehabbing him from a torture camp. Most fearful dogs just need to learn how to trust a human again and a good structured schedule, lots of love and endless patience and distracting the dog from his fears in a good life-enrichment program will help this dog come to learn his can trust you and teach him that his new life is full of good work, learning and positive reinforcement and in time, the two of you will form a bond that makes a great team.
Here is a recent thread with a dog with anxiety issues - from different causes - but whatever is causing the fear and anxiety - the rehabilitation treatment is the same as is outlined on that thread:
http://www.yorkietalk.com/forums/gen...ty-issues.html