Answer: The native eastern white cedar, Thuja occidentalis, fits all your criteria. It grows naturally in the northern forest, so you'll probably find them on the church property. The species found wild in the woods can grow quite tall, though. There are lots of cultivated varieties that are chosen for their various growth habits, including compact and narrow varieties, and in a varieties in colors from dark green to yellow. This tree also seems very appropriate for a memorial, as one common name for the tree is arborvitae -- the tree of life.
The best time for planting is spring, as the trees will have the whole summer to settle in. Be sure to wait until the soil has drained sufficiently to work -- otherwise you risk compacting the clay to the point where it's impossible for the trees' roots to penetrate. For best results with your investment in trees and labor, see if you can find a landscaper or nursery worker to advise you on planting.
As for deer...they will feast on the bark and twig ends in the winter. The best protection is a sturdy fence, but some brands of deer repellent have shown good effect. Look for Deer Away and Deer Off -- I've heard great things about them.
Finally, here's a link to some images. Please keep in mind that there are probably over a hundred named varieties that look quite different from these images:
Best of luck!
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