I've read somewhere (WaPo? Politico? Stratfor? Here?) that one of the things that dissuade Putin was that he was informed that the West knows where he is - and a nuke would trigger an overwhelming attack on wherever that was. He backed down because he was convinced that doing it meant he'd die. Was that way off base? Just a rumor? Someone's wishful thinking? I'd expect that our intelligence services have a good notion of where he is at least most of the time.