The British did not trust soldiers alone to hold this gap. In 1832, Ensign John Peyton Jones of the 63rd Regiment proposed a cruder, more terrifying deterrent: a row of dogs chained across the isthmus, close enough to raise the alarm together but not quite close enough to fight one another. The Dog Line began with around nine animals and grew over time to as many as eighteen, a mix of breeds chosen for their ferocity. Lamps stood behind them so sentries could see anyone who tried to slip past in the dark. Some accounts placed dogs on platforms in the shallows as well, to close the gaps at the water's edge. The message to the convicts of Port Arthur was deliberate and constant: this way out is closed, and it has teeth.

Thomas Lempriere, a commissary officer at Port Arthur, declared Eaglehawk Neck simply impassable. The convicts disagreed, and a few proved him wrong. The bushranger Martin Cash, perhaps the most famous escapee of the era, got past the dogs by wading and swimming around the line out in the sea rather than testing it head-on. Guards spread rumours of sharks in the bay to discourage exactly this kind of attempt, and the water was bitterly cold besides. These were desperate gambles, and most who tried were caught. The punishments for recapture were severe, from floggings to time in the Separate Prison's silent cells. But the very existence of the Dog Line is a measure of something the records sometimes obscure: the men held on this peninsula never stopped trying to be free, and some were willing to risk cold water, sharks, and the lash for even a slim chance at it. The Neck was not impassable. It was simply designed to make the attempt feel like madness.

The convict story is only half of why people come here now. Just south of the Neck, along Blowhole Road, the Tasman Sea has spent millennia carving the coastline into something theatrical. The Tasman Arch is a vast natural bridge of dolerite, the roof of a collapsed sea cave that swallows the swell beneath it. Nearby, the Devils Kitchen is a deep, raw chasm where the same collapse went further and left only a churning slot of water far below. A booming blowhole completes the set. These formations share a single origin: relentless ocean attacking cracks in hard rock until cave became arch and arch became canyon. It is the same patient force that, a little further along the shore, produced the famous Tessellated Pavement.

Today the menace has drained out of Eaglehawk Neck, and what remains is a small coastal community wrapped around one of the prettiest beaches on the peninsula. The place was formally dual-named Teralina in 2021, restoring the original name alongside the colonial one. The long curve of Pirates Bay draws surfers to its eastern side, and in summer the population swells as families return to holiday shacks scattered along the shore. Clyde Island, at the bay's northern entrance, can be reached on foot at low tide and hides two old graves and a rumbling blowhole that splits the rock. The guards' quarters near the isthmus survive as a small museum, the last built reminder of the years when this beautiful, ordinary-looking gap was the most closely watched ground in Van Diemen's Land. Stand here on a bright summer afternoon, with children in the shallows and surfers beyond the break, and the contrast with the island's history could hardly be sharper.