Many gardeners make the mistake of planting leyland cypress only 6-8 foot apart. Leyland demands a wider 16-18 foot spacing. Unfortunately, leyland is also susceptible to 3 fungal needle blight diseases. Diseases usually don't infect until shrubs are 10 years and older. There are no practical cures (pesticides) for these diseases. Over time the shrubs may need to be removed at a considerable cost to you.
If you must grow tall screens or hedges, I recommend the more dependable Japanese cedar (Cryptomeria japonica) or Green Giant arborvitae (Thuja x plicata). In the 20-25 foot height category, plant Nellie R. Stevens holly, Foster#2 holly and Emerald arborvitae (Thuja occidentalis 'Smaragd').
Some great evergreen choices in the 10-15 foot range are leatherleaf viburnum (Viburnum rhytidophyllum), skip laurel (Prunus laurocerasus 'Schipkaensis') and 'Hick's Yew (Taxus x media 'Hicksii').