Why does Riley do this?¿?

Ok, Riley sleeps in my room at night. He will never use the bathroom on my bed, but will on my brother's bed. He doesn't like my brother, every time he comes near him he will growl and start chasing him. Is it the scent that makes him insecure, so that he'll leave his scent there? :confused: I'm not sure, but I get in a whole lot of trouble when he does. Thanks in advance.

It may be a dominance thing, but once they urinate in a spot, they tend to go back there because of the scent. So, if his bed hasn't been throughly cleaned and "descented" somehow (we use Simple Solution from Petsmart) the dog will probably return.