With a tent and an airbed packed into his old silver Mercedes-Benz, and a kayak strapped on top, overstayer Jurgen Karl Ahrens made the New Zealand outdoors his home.

For 20 years, the 72-year-old German avoided authorities and deportation back to his home country because he was always on the move.

Often police would turn up to a sighting not long after Ahrens had left.

This week, Ahrens' luck ran out when he was finally sent home.

Wanted for questioning over an assault in Fox Glacier in 2004, he had been spotted by a member of the public at Aoraki-Mt Cook National Park and was arrested by police as he was about to go out kayaking on the Tasman Glacier.

"He had been in the hills for a couple of days when we picked him up, so he was unshaven and pretty scruffy looking," said Constable Joe Rush, a Twizel policeman who dealt with Ahrens.

"He said he used to take his sleeping bag and just go walking and sleep under the stars somewhere. He had a great general knowledge of the South Island - he must have been to every little nook and cranny. He was actually quite interesting to talk to."

Mr Rush said police initially wanted to talk to Ahrens only about the 2004 assault complaint. "We did some inquiries with Immigration about his status, and that started to open up a can of worms, really."

When Ahrens dealt with people over the years he used another name - he said it was because he got tired of people being unable to pronounce or spell his real name. He had a New Zealand driver's licence in his real name.

"He was a very polite gentleman. He was no problem whatsoever to deal with," Mr Rush said.

Ahrens claimed to have spent some time living in a flat in Christchurch, but police could not find proof of this.

"He said he travelled a lot. He had a tent and an airbed, and he just goes everywhere, from what he said to us. He spent a lot of time in Department of Conservation areas, just exploring New Zealand," Mr Rush said.

Ahrens told police he coped financially by collecting the German pension.

Immigration New Zealand would not discuss the Ahrens case, but said its upgraded systems had led to the number of overstayers falling 29 per cent since 2004.

In the year to June 30 last year, 2087 overstayers left the country as the result of Immigration NZ action.