If I had the space, and the 200T of flint,
I would be very tempted by the gabions,
especially if you incorporated some planting pockets in them for instant plant life.
As it a boundary, have you considered nature's barbed wire,
a decent, fruitful blackberry?
You can easily get 3 or 4 metres of growth of fruiting stems each year,
which are easily tied onto stakes.
If I had the space, and the 200T of flint,
I would be very tempted by the gabions,
especially if you incorporated some planting pockets in them for instant plant life.