Where do I go to buy a Watch Dog?

You can't buy a Watch Dog anywhere because
1) they are born WILD (野狗).
2) no shop will stock up any product that all people hate.

Watch dogs are not obedient because they are always out of control. They just know barking to anybody passing by without any reason. If they keep on barking at you, try to say English to them. I believe most of them are not educated or trained to understand English.