Ahhh...the old, casuarina hedge in front of a chainlink fence...
See a lot of this over here.
What is your goal? do they want you to try and renovate it, make it thicker all over?
If so, that will be quite difficult as the lower portion of the hedge has been allowed to get mature, hence the thick trunks and sparse lower foliage. The top is typical, probably been macheted year after year, see the thick growth on top, and the accumulation of dead needles just below. all the regenerating growth has been concentrated in the top, with the lower portion being shaded out and getting sparser and sparser.
Depending on the amount of branching in the lower portion, it can be cut back HARD, almost topped really, about the only time I would even suggest this, casuarina sprouts quite vigourously with watersprouts and epicormics after a hard cut back...of course the risk is that the 'parent tree' are too old and tired to regenerate sufficiently.
Looking at the thickness of the trunks if you have the time, try cutting a couple back real hard to reasonable sized lateral and see how they do...otherwise if they are looking for thick lush growth top to bottom fairly soon they'd be better off ripping the whole lot out and starting again. For a thick hedge we plant new trees at 2' centres, and formative prune to ensure branching from as low as possible
Its important to maintain that tapered out shape to ensure light gets to the whole surface, top to bottom, shearing them with a machete inevitably ends up with an inverted shape that shades out the bottom...
Treeseer, casuarinas make very good tight hedges, respond well to shearing year after year, and the odd hard prune to maintain a good scaffold. They hold up well in dry conditions and tolerate a good amount of wind and salt spray.