I inherited 3/4 of a mile of Leylandii bordering our sheep field when I bought the farm - nasty stuff and as you say grows out of control - it was 20 foot plus in places and only going upwards 
. Ideally I'd fell the lot and plant indigenous blackthorn, but I need the shelter for the sheep, and the new fence would take ages to mature. So I cut the lot down to 4 foot 6 inches, and each year since, I've run a tractor mounted hedge flail down it. It's grown into a decent thick bit of shelter but needs regular attention. The trimmings made an enormous bonfire
. Ideally I'd fell the lot and plant indigenous blackthorn, but I need the shelter for the sheep, and the new fence would take ages to mature. So I cut the lot down to 4 foot 6 inches, and each year since, I've run a tractor mounted hedge flail down it. It's grown into a decent thick bit of shelter but needs regular attention. The trimmings made an enormous bonfire
