I see from 4Corners post that I read the original post too quickly and missed the part that the willows must remain. Whoops on my part.
That being said, I like 4Corners idea to fit different trees behind the willows if at all possible.
If not, are you on good terms with your neighbor? Would they agree to a screening hedge on THEIR side of the property line if you contributed partly to the cost, or watering, or etc.? It (usually) never hurts to ask.
