male dogs scenting

My brothers dog has started spraying indoors up sofas walls and anything else he might want to he is house trained there is two other female dogs in the the house any idea as to how to stop him from spraying

Oh dear not had this problem,guess could be of females, best washed in Biological washing powder with warm water. This breaks down enzymes so he wont smell where he has been so will stop him gong in same places

Could the females be in season? Heard of a cat spraying but never a dog i would ask the vet but it may be a way to say its my house