You MUST clean the area. Then finish off by putting vinegar all over the area. (This marks the area as YOURS, not his.)
Then TAKE the dog out where you want it to do the job.
We have a new lap dog...supposed to be more difficult to train than larger dogs....but with love and direction, she only uses the area she is supposed to use.
When it is raining and she doesn't want to go to her area I just say 'finish' and she runs around the corner and does her job.