Thanks Braham.

Your map shows the dog fence running north almost to the Gulf of Carpentaria. I suspect it is innacurate. As the entire fence is yet to be officially surveyed, it is hard to find detailed maps on the web (without paying). I used an overlay from a Queensland Government map but it still lacks in detail.

http://www.nrm.qld.gov.au/pests/maps/barrier_fence_maps.html

There are many vermin barriers in Australia and there are more dog fences further north. They may have once been part of the main fence which may explain why the fence runs further north in your map.