TLK

I understand that watch dog is allowed .. but what is the exact ruling ..

1. if you touch the dog (skin) would you become Najs?

2. how about the saliva of dog, Is there a limit that would make your clotes najs, like if Dog comes and lick u, and the size of drool/saliva spot is less than a penny, do you still need to change your clothes.

3. I also understand that dog needs to remain outside the house.

but can some one provide me with rulings or links where I can read in details.

Point is, I want a watch dog for my daugters (5 and 2 yrs old), cause I am very paranoid about there safety, specialy when they are playing outside on the street, i want the dog to guard them