Posted: 16/11/2016 at 15:52
Hello and welcome Josh
There's an old saying 'Growth follows the knife' meaning that pruning stimulates growth. In late January (i.e. before bird nesting time) I would cut the side of the hedge back and feed the base of the hedge with some Fish, Blood and Bone meal which is a slow release organic fertiliser. (it won't do your dog any harm - some dogs eat it!).
If possible try to shape the hedge so that it's a bit wider at the bottom than the top .... an A shape ... this means that the base of the hedge won't be shaded by the top and the sunlight will also stimulate growth.
Privet is a pretty tough plant and benefits from a good cutting back every now and then, so don't be afraid - go for it.