I have found several different sources on the internet that give different figures for the length of these two fences. For example, the Great Wall of China is said to be 2400 km or 6400 km or 6700 km or even 7200 km or more.

The Dog Fence, or Dingo fence in Australia (also known as the Barrier Fence, or the Wild Dog Barrier Fence), extends across the south east corner of Australia, and its length is given by different sources as 4000 km, 5000 km, 3200-5800 miles, 5500 km, and even 8500 km. Some also claim that the Dog Fence is more than twice as long as the Great Wall of China.

I would like to know:
1. Which is longer?
2. Why are the so many different distances quoted for the Dog Fence? The Great Wall is partly in ruins, and has a lot of complicated features, so it is clear why there might be some confusion about its length. But the Dog Fence is much more straightforward, and should be very easy to measure.
kurdiatcha, that is very impressive. I just ran across the Dog Fence on the internet. Everybody has heard about the Rabbit-proof fences in Australia, but I had not heard of the Dog Fence before and I started to read about it (the internet is an amazing thing). I soon became astounded because the Dog Fence seemed to have different names in different states, and places. Also, although there was a lot of bragging about how it was the longest man-made structure on earth, the quoted lengths of the Dog Fence varied by a factor of 4 or more. I was astounded that something that recent would be that hard to measure. After all, since the Great Wall is thousands of years old and partly in ruins, one might expect some difficulties, but not with something just a bit over 100 years old (I thought). Of course, all the pictures I found made the fence look very well maintained and simple.

That is a great answer. Thank you.

Can’t help you with the distance measures. As you say, they vary. Can help you with the second.

The dog fence isn’t more straightforward, in fact it’s even more complicated than the Great Wall. At least the wall was constructed as a single unit with a single purpose, and by one organising body.

The dog fence was constructed as multiple units. It started initially as dozens if not hundreds of property fences. Individual stations would fence out dogs comingin from their neighbours and from adjoining bush. Even more commonly stations would dog-proof their weaning and lambing paddocks, since it was lambs, lambing ewes and weaners that are most vulnerable to dog attack.

So before anyone even thought of the dog fence we had hundreds of kilometres of dog-proof fence in that part of the world. The longest section was probably no more than 50km on a side and most sections would only be 3 or 4 kilometres to a side.

Over time neighbours realised it was more efficient to join up their dog fencing on a long front rather than trying to fence off individual staions or paddocks. So we started to get many stretches that were hundreds of kilometres in length. But still no dog fence.

Then someone got the idea to make the fenceline ‘official’ as it were, and extend it between gaps in the existing fenceline. But the official construction was funded in patches, with funding often being dropped for several years at a time. And the fences decay over time, so by the time the fence had been ‘officially’ constructed all the way to Hughenden the South Australian end was in tatters.

The fence has been sporadically repaired ever since it was completed, sometimes by state governments, sometimes by local councils, sometimes by landholder groups but usually by individual landholders. But large sections have never been repaired since they were built and now exist only 5 strand wire fence that will stop a sheep or cow, but not a dog. In the worst sections the fence has been quite buried by sand dunes and only the top few inches of the posts stick out in places. Dogs simply walk over the top.

A major source of confusion is that nobody is entirely sure what the official dog fence is or where it runs, The SA and NSW governments both had their own dog fences, but various regional bodies and local governments also had dog fences. All these different fences join up or once joined up, but they also quite often branched and forked. As a result you will sometimes see maps of the dog fence that end at Hughenden in Northwest Queensland and sometimes it ends 100o km in the opposite direction at Jandowae in SouthEast Queensland. Sometimes the other end terminates at Talatal in SE SA, and sometimes at various different stations in NE SA. As a result you will get wildly different answers depending on what sections you wish to include.

To add to the confusion there were sections of the fence that, due to apathy, environment and administrative oversite were never finished. They exist on the plans but never existed in reality.

Then just to make it worse at various times people have cut corners off the fence or swung it back on itself. In at least one case an entire section of the fence became an island as two stations ran their own fence between their cornerposts across bushland.

The final confusion factor is due to scaling problems. Have you looked at a map of the fence? It isn’t anything like straight, instead it wanders across the countryside like a drunkards walk, following watercourses, property boundaries and old paddock fences. As a result you get totally different figures depending on what scale you measure at. If you simply draw a line from the southwestern to the northeasternost points it’s only about 1000km. But if you were to run a tape measure from post to post along the entire official fenceline it’s over 7000km. I hope that makes some sort of sense. It’s the same problem we get measuring river lengths. As the crow flies the Amazon for example is only about 2000kms from mouth to source, but if you were to paddle up it you would cover over 6000km.

So as you can see it’s almost impossible to determine how long the fence is. The continuous length that will actually stop a dog varies year to year as repair work is done and the length of those bits will vary depending on how you choose to measure it, and it isn’t even clear what bits to include in the measure in places where the fence forks. The longest distances are for the total lenth of wire needed to fence the ‘official’ fencline, regardles of current state of repair, along the longest possible route form Yalata to Jandowae. Shorter figures incorporate only sections capable of stopping a dog or take alternate routes to Hughenden or stop in NE SA or various other variations or simply measure at a coarser scale.

It all depends on what your definition of "is" is.