My lil' Yorkie only humps blankets and fleece.
I couldn't stop him, so I went to PetSmart and asked a trainer.
She told me to pick up a little spray bottle and just put water in it.
Whenever he humps, she told me to spray him in the chest or shoulder area.
It has been 2-3 days and he has not humped since *knock on wood*.
They said do NOT spray a Yorkie in the face, because they are so little they will get timid and very very scared.
Try it, it worked wonders for me!
Let me know if it works.
Boa Sorte (Good luck)!