urinating (marking)

Question
We have two families that animal-sit for each other.  The dogs are quite used to both homes.  One neutered male Bichon-Shitzu (about 6 years old) will spray mark in my home whenever he gets a chance.  He does not do this in his own home.  His own home has two female dog (spayed) and our home has one spayed female dog.  How do I stop him from marking my furniture and walls??

Answer
This dog is definitely claiming territory.  The only way to stop this behavior is to put him on very long, lightweight indoor leash and observe him closely.  Dogs sidle up to objects before lifting their leg; if you see this behavior, interrupt it (clap your hands, bang on a table, don't direct any verbal correction at the dog and don't make a sound so loud as to startle the other dogs.)  Once he stops (and he should immediately), rein him in, ask him to "sit", praise him and go back to normal.  Even confining him to another room won't stop his marking (in fact, may escalate it.)  He will learn not to lift his leg in your home.  If you had caught him in the act the first time, a simply "Nah!" would most likely have inhibited him and he would have been a lot less likely to repeat the behavior; it's too late for that now.  Asking him to "sit" before feeding him, petting him, etc. in your home throughout his stay will also promote you psychologically and make him calmer (because you are in control).