Ilex glabra, Inkberry, is a native evergreen holly that is fine with wet conditions. Not sure if you have specific height requirements though.

I was just here checking another post when I saw yours. I would suggest White Cedar they can handle just about anything. They've seen temp extremes at my house from -30 to over 100 with no foliage damage. The only thing that bugs them is SALT! But I dont think that would be a problem for you. Thuja green giant is a good choice. The only thing I don't know is how well they deal with dense clay. But they grow in gravely soil so it seems likely they could handle the other extreme.

American Arborvitae (thuja occidentalis), Florida anise, and wax myrtles will tolerate those conditions. The arborvitae would come closest to looking like your leylands. Just as a note, I am assuming that this soil is not squishy wet all the time. From past experience, I would advise you to plant the arborvitae high in the hole.

There are only 3 types of cedars that are recommended for the south: Atlas, Deodar, and libani. Big difference between zone 4/5 and 7b. (No offense, greg.)

Dahoon holly. Grows almost as tall as your Leylands, has red berries on the ladies if you plant one of each. Not as dense as leylands but dense enough.

Sorry Donna but it is you who are wrong, about White Cedar at least. They do very well in Atlanta (Z 7b) they are just the devil to find in a nursery. Too bad, because they would be perfect for Koosh's situation. Really there is no other needled evergreen that is suitable, though Bald Cypress and Pond Cypress are conifers that would be good, just not evergreen.

I believe that what greg is referring to is: Chamaecyparis thyoides (Atlantic White Cypress or Atlantic White cedar)