What is the Shar'i ruling on keeping a guard dog at home, and does it prevent angels from entering a house that a dog enters, and what is the ruling on praying in rooms other than those the dog enters, and how does one purify oneself after playing with the dog?

If the dog is permitted [to be kept], then there is no harm in bringing it into the house for a legitimate purpose, such as training it or introducing it to the family members. The place entered by the dog does not become impure unless something from its secretions falls onto it. In that case, it must be purified with seven washes, one of which is with earth or soap. The mere entry of a dog into the house or a room does not prevent prayer in it, unless something from its bodily secretions touches it.