Why do you suppose my boy wants to pee on (and tries every time) a bitch of the same breed he meets occasionally on walks? They are both entire, he is currently 'tardeked'. I am supposing it is hormonal and he has taken a real shine to her.
I have known of dogs doing this - I used to walk a Border Terrier bitch and once stopped to talk to a guy with a beautiful BSD male. The BSD promptly peed all over poor Meg! My personal theory is he is "marking" the bitch as his as he doesn't want anyone else to have her!!!
My boy regularly pees on his mums head ;-) Mind you, she has stopped to sniff where one of my other bitches has peed and I think he is trying to pee on that, not his mum. She just gets in the way :-D