Nice wind break Mark, but be aware that Leylandii Cypress only last about 25 years or so and get very leggy if not pruned annually!
Never pruned these, in fact you'll screw them up if you do. I use them as Christmas trees and yes those get sheared twice a year.....but that's apples and orangeLeylandii's.
Once staked their big roots will go to China. They anchor well in my clay loam and I've had 6" rain and straight line winds.
Something you're doing is not right. Perhaps it's your sand?
Do these look leggy to you? I planted pines at the same time in between. They have been choked out.
25 years or so? Could care less. I'll be in a retirement home by then.
For stately trees that will go to 500 yrs. + I put in dozens of oaks and maple.