[Jespah]

It sounds like he's marking. Just like outside, if he's in another territory or his own, he is letting the other dogs know he was there. As, you maybe aware from your walks with him, it's not that he has to go, it's that he wants to make his mark. I know Rupert will do his thing all over the neighbourhood, and even lift his leg and "go through the motions" when he's empty.