Thuja- thickening up

I planted 60 Thuja 3 years ago when about 4ft high. In the main they are now 7-8ft. What they are not doing, in proportion, is thickening up by side growth. How can this be encouraged. Would cutting the front and back be best or would as with some plants nipping out the top but I dont want to stop it growing up, its to hide nasty neighbours you see.

Bernie

 

Luckily, Thuja can be clipped back harder than Leylandii, which often die back if pruned too hard.
The leader can be cut back as well to bushen up the side branches, however, it is better to do this when the leader hasn't gotten too thick.
Tip back the leaders new growth and give all the side branches a bit of the same. Do this every year, and they should bush up fine.

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