Take a little hike around the 'wild' areas near you and see what grows naturally in the canopy, and has leaves at this time of year. Look for spots with similar amounts of light/shade as your fence line area.
You might even get lucky and encounter seedlings you could transplant, as long as it's not a protected species.
Another thought was the wild rhododendrons with the purple flowers. My parents had a large planting of them in Vancouver BC, and they grow wild in Manning Park, too. They will definitely get to be well over 10ft. tall. Great screen plant and beautiful when in bloom. You can start them from layering the lower branches, pinning them to the ground and letting them root.
