I always have trouble with hand held night-time shots, and I only had a couple of seconds before the crafty fellow disappeared. Out little doggy was shouting at the girl-fox on the lawn, so I went back in the house to grab my camera and suddenly spotted the brother up on the roof of our gazebo when I came back out.
Fruity, I can’t judge how near your gazebo is the the fencing. Is it possible the fox leaped from the fence tops?
Otherwise, have you a log pile or any next to the gazebo he would have used as a stepping stone?
I would be very surprised if he got up there from ground level.