Es tan simple como "buen perro", aunque es muy común usar "buen chico" también.

I usually say to my dog... buen chico (good dog) y perro malo (bad dog) Chico/chica is in english boy/girl but in my country is common to use these also when you talk to a dog.

ugly --> angry

you need say "buen perro :) " or "perro malo, perro malo" and after look ugly while put your left hand in your waist and shake your index finger by your righ hand