My little boy chihuahua (Tinker) should be Stinker - he occasionally tries to "mark" in the house, especially one corner of my white bedspread. :?
I bought a product called Urine Trouble (by the same company that makes Mary Ellen's Best Press) and it does a good job of breaking down all the chemicals in the urine so that they don't attract the dog back to that same spot. It gets out the stains and spots, too.
There are other brands that use the same kinds of enzymes to remove the chemicals that attract animals, just look in the carpet cleaning section of your grocery store. Febreze makes one, Resolve makes one - check the label to see if it has these cleaning enzymes.
I wish I could find some way of training a dog not to mark - I love my pets but this is the one thing I can't handle - eliminating in the house.