If a dog's saliva touches you or your clothes or the place where you pray, you're not fit for salah. Dogs are allowed for guarding purposes only, and you're supposed to keep away from them, not cuddle up with them and let them lick your faces like you must've seen many people do. Also the angels of mercy don't enter that house. Rasulallah (saw)'s grandchildren Hassan and Hussain (raa) had a dog, but they kept it outside or in a doghouse. Once the dog entered Rasulallah (saw)'s house, and he led it outside and poured water on the place where the dog had sat.