Living in the arctic, much of our winter activities have to be quick so we can get back inside after a short while. Outside of jogging with me in the mornings and doing some light disc work, most of our winter work is drag weight training or the spring pole.
Kayden's days of competing in weight pull are over, but we still do a session or two of drag weight training each week to work on building some strength and endurance. You get a lot of odd looks hiking down a trail with your dog pulling a tire or two, but it's great when you don't have a lot of time. Usually 15 minutes of pulling and he is gassed.

We also have a spring pole for him in our garage and I usually put him up on it for 15 minutes or so while I'm clearing the driveway. I keep it low enough in the garage so that he can easily touch which helps to put more of the focus on his rear.
He looks a little possessed in this picture but he's just havin fun
