AAAHHHHHHH!!!!!!!!!!!

Question
I have an 8 month old Shih Tzu puppy who was, believe it or not, COMPLETELY house trained. He never did his business indoors! And believe me when I say this took quite some doing. I say he WAS house trained that is until my mother in law baby sat for my husband and me one night about a week ago and brought with her her male dog who decided to mark his territory all over my living room!!!!!! Now my once innocent puppy walks around the living room with his nose to the floor sniffing and peeing EVERYWHERE! I catch him in the act and take him immediately outside to finish where he looks at me as if I have committed a terrible crime and flops down on the grass in protest.I pick him up and put him back on his feet until he finally gives in and finishes his business.An hour or two later it starts all over again. (grrr)I purchased some spray that is supposed to take out all the doggie odor but he still finds those spots even though I (thank goodness) can't smell anything. There are no less than eight of these spots , one of which is on the arm of my new suede sofa!!  Incidentally , my mother in law seems to think it's all quite funny. >:|  

Answer
My answer is not one that your going to like much, and it's not really that of an expert.  But, once one little male potties in the house then the other thinks it is his DUTY to reclaim what is his by Remarking it as HIS! the only way to know for sure where the other male went and clean up the odor for good is to try some products from Petsmart like the UV Light Stink Finder and then use "Get Serious" pet stain and pheromone odor remover. And continue taking him out to use the potty and while he is inside you may want to try keeping a belly band on him to keep him from remarking anything else inside the home until you get everything cleaned up in the meantime.  Good luck and hope this helps out some. Oh and by the way, unless you plan on breeding this little guy you may want to have him neutered... because  he will continue to mark this is a territorial thing and not a potty thing in most cases and if you get him neutered it is a behavior that can be controlled.