[BellaDonna]

I purchased the pet repeller as well and so far I really like it. It does seem to have more of an affect on some than it does others. One of my chi's hates it and will leave the room completely.
I just touch the button for a split second usually to get their attention so I can say stop.
The bad thing about tiny dogs is that they are hard to catch and hard to get your hands on when they are yapping. You don't want to chase them around like a psycho. If they were close to us we could redirect them by hand on something.
One thing I saw on Dog Whisperer was to put the Yorkie on a long lead like 25 ft or so then take them to the area where they most tend to bark.
That way you can actually get hold of the lead and give them a quick correction while you are saying ENOUGH or NO or whatever you say.
I do have good luck with the pet repeller though and it has already made some difference in the way they bark.