dog pooping on carpet

Question
I have a maltese/poodle cross about 7 years old.  In the last few years he has developed an annoying habit of using the corner of my white persian livingroom carpet as a bathroom when we are at work.  We have spanked him to no effect.  When we are home the living room is actually an off-limits area for him.  If we lock him in the laundry room for the day while we are at work (which I hate to do)he does not have any accidents so it is not because he cannot hold it, in fact he is never even in much of a hurry to get outside to do his business when we get home.  Any ideas how to break him of this.

Answer
As you have seen, the spanking doesn't do any good.  Any discipline when you don't catch the dog in the act is useless.  It may be showing you he can go in the living room.  Obedience training along with neutering if not already might solve the problem.  

Likely you will have to fall back on locking him in the laundry room.