The Dingo Fence or Dog Fence is a pest-exclusion fence that was built in Australia during the 1880s and finished in 1885, to keep dingoes out of the relatively fertile south-east part of the continent (where they had largely been exterminated) and protect the sheep flocks of southern Queensland.

It is one of the longest structures in the world. It stretches 5,614 kilometres (3,488 mi) from Jimbour on the Darling Downs near Dalby through thousands of kilometres of arid land ending west of Eyre peninsula on cliffs of the Nullarbor Plain above the Great Australian Bight near Nundroo.

It has been partly successful, though dingoes can still be found in parts of the southern states. Although the fence has helped reduce losses of sheep to predators, this has been countered by holes in fences found in the 1990s through which dingo offspring have passed and by increased pasture competition from rabbits and kangaroos.

More Info: en.wikipedia.org