well you can start with a
DEAD hedge with the plan of having it turn into a living hedge.....
that seems to be what you are already suggesting with the idea of piling eucalyptus branches, only i would try to scavenge up a lot more trimmings from where ever else too, thorny stuff especially, to add to the bulk of the initial dead hedge.
then plant climbers and hedge plants all around it and slowly they take over as the dead hedge degrades. and if the dead hedge is thorny and thick enough, it will protect the young plants that are getting established to take over the hedge eventually. a nursery of sorts, being protected by the dead hedge.
some suggestions for planting: rose, berries, trees that coppice, plums, wild grapes, hazelnut, climbers and thorny vines
you could also do this with a simple fence too, and then use that as a base for the emerging living fence. eventually a wooden fence would rot, and hopefully by that time the living hedge will have filled in enough. this is the method i have used more, but i like the idea of the dead hedge and i would try that out in a certain circumstance.