My little Yorkie has the best 'nose' of any dog I've ever had! The other night he wanted out at 1AM, I opened the door and he shot out like a rocket!
When I walked into the yard, [no fence] he was nose to nose with a MASTIFF!! He knew it was out there.
I walked up slowly, saying 'good boy' over and over and grabbed Piper up by the skin of his back, lol. The Mastiff was wagging but you never know.