Answer: The shrubby dogwood (Cornus sericea) is quite dense so it would be a possible choice. You should be aware that it tends to sucker and spread by underground stolons so it is not a particularly tidy plant. The smoke bush (Cotinus coggygria) in my experience grows more as a straggly half tree than a uniform shrub, so it would be perhaps less effective. I am not sure which elder you have in mind, but most of the elders require a very moist soil to do well, so that is an important consideration.
You might wish to consider some of the viburnums which, although not as fast growing, are generally more attractive plants throughout the year. Another possibility for even quicker cover in partial shade is to grow vines on a fence or strategically placed trellis panel.
Good luck with your screening!
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