Great trellis - Tips on growing clematis--did you know they can't climb wooden trellises? They don't twine; they wrap, so any support thicker than inch won't work. Use twine or trellis netting to give the illusion of climbing on your wooden trellis.
How to Build a Fence Mounted Trellis - Cut a 5 x 10 foot piece of rigid wire mesh. Attach four wood blocks to the fence (one for each corner of mesh), screw a hook into each block, and fit the mesh over the hooks.