That annoys me too. At the moment I have a Numidian spy sitting outside the gates of Alexandria. He just will not go away. I've popped him out on his ear twice. I've tried assassinating him on several occasions but he must have a trait giving him added protection and my assassins die. I have tried to spy on him but my spies also end up dead. Who is he, the Numidian version of James Bond!. I am hoping the very fact I know he is there (being visible on the map/sending agents against him) will render the spy inoperative, i.e not allow him to re-enter the city while he is visible. Is this a fact or am I just spewing rubbish again.