Hi Minskey, I must admit I sell Leylands (steps back from all the boos) but I do only sell them as a last resort, or if the customer absolutely insists on them!
Silly question, when you bought them, were they pot-grown, or dug-up and transplanted? If it was the latter, that's why you're having probs. Leylands won't transplant from open-ground as they are so shallow-rooting, they don't form a rootball like 'normal' conifers, so a 5' tree should have a 5' diameter root - don't fancy digging a hole that wide