My 1.5 year old neutered male cockapoo has begun to mark in the house. Buckland has been housetrained successfully for nearly a year. He is a very social pup and enjoys being with the family. The entire process is very strange: he will leave the room where the family is and go upstairs alone. He will then do his marking on either of my sons' bedroom rugs and come back downstairs. At first I thought he hadn't been out often enough, so we've been taking him out more often. Last night, after he went out, he disappeared and marked my son's bedroom carpet for the second time in a week (different spot). This is the fourth time he's done this in 2 weeks, with the last two being on consecutive nights (2 different rooms). We're keeping the gate up and watching him more closely, but I'm wondering what the root of the problem may be. It doesn't seem normal that he's become "unhousetrained". He is not under stress as the vet asked. Any suggestions? He is acting normally otherwise. Thank you for your help!