"You do some very odd jobs in archaeology. I did a job once where I almost lost consciousness. That was very interesting."
He was digging out a well that time. A well can be interesting in itself, and it can also be used as a pit for colonial rubbish. As he went deeper the amount of carbon dioxide built up, and he had to be pulled out.
"The deepest well I have dug was something like 16m, but it was dug in stages, with a mechanical digger, so you could step down into it."
David got interested in military archaeology while he was at Auckland University. He and other students were paid to help excavate the former Albert Barracks, a large star-shaped fort built as a potential refuge for settlers if the Northern War reached Auckland. It would have been similar to the Rutland and York stockades in Whanganui, only bigger.
He ended up analysing its British and colonial military artefacts, and still gets consulted about such objects.
The dig was really good fun, he said. He majored in archaeology, graduating with a MA (hons) in 2003. He learned to use mapping equipment that records information in three dimensions, and equipment that picks up whether soil has been disturbed, without digging it.
"You need that in urupa, to find unmarked graves. It would be inappropriate to dig test pits."
He could have carried on to get a PhD, but left university to become a consultant archaeologist. He worked on many digs over the next eight years.
He's dug early Māori sites - sometimes called "moa hunter" - and later ones. He's found moa bones, moa gizzard stones, fish hooks, adzes and pounamu (greenstone) objects. On later sites he's found coins, jewellery, bottles and broken crockery.
The first site he worked on after university was a pa about to be destroyed by a quarry near Tauranga. Te Oropuriri, at Bell Block, is one of his favourite dig memories. He was fascinated by the maze-like entrenchment system of its gunfighter pa.
"Everything about that site was incredible. It was a very rich site."
It was also big, complicated and multilayered. His musket finds were in a bell-shaped rua, a pit with a narrow entrance that widened underground.
Such rua were often dug by children and used to store things. The objects could be food, or valuables, sometimes stored in kete. One rua at Te Oropuriri contained gunpowder flasks.
"There were multiple rua, and they were all full of stuff."
After his time moving around David got a regional archaeologist job with the New Zealand Historic Places Trust, now Heritage New Zealand (HNZ). For five years he was the archaeologist for Hawke's Bay, the East Coast, Wairarapa and the top of the South Island.
His job was to police and review any archaeologists working there, chase down people damaging sites and liaise with councils.
While there, unpaid and out of his own interest, he started an email series about 150-year anniversaries. It spanned the time of the New Zealand Wars. There are dates significant to Titokowaru's 1868 campaign coming up next year.
In 2014 Prime Minister John Key talked up New Zealand's "uniquely peaceful" beginning. David says it's a myth.
"Say what? In the Musket Wars alone there were about 50,000 people killed and about 30,000 enslaved."
He hasn't had as much work as he would like since moving to Whanganui.
He's been consulted about a cannonball, and about traces of Māori agriculture and railway remains for a person selling land near Patea. He did a few weeks work for Whanganui Regional Museum and some for Aotea Utanganui, the Museum of South Taranaki.
He tagged along when Michael Taylor and Annetta Sutton went looking for a redoubt site they'd heard about near Kai Iwi. They found an early Māori site instead.
But there's more to come. David's trained eye has spotted shell midden weathering out of the Whanganui River bank near the City Bridge. And when the Sarjeant Gallery extension goes ahead the site will overlap the Rutland Stockade - mainly the former quarters for married men, later taken over by squatters and burned down to clear them out.
When there's no paid work David makes short videos about archaeology and military history, and puts them on YouTube. He's called the series Archaeonomy. There are 32 videos so far, starting from the general and moving to the particular.
His A Virtual Tour of New Zealand Archaeological Sites: Part 4 concentrates on sites in Ngā Ruahine leader Titokowaru's South Taranaki campaign, which reached almost to Whanganui.
The most popular clips have had about 200 views, often by people overseas. He's not making money from them, but wants to raise the profile of archaeology.
He's also done some unpaid site recording around Whanganui. There are a lot of unrecorded sites here, he said, mainly 19th century ones, but some pa as well.
Archaeological sites are documented in different ways. The New Zealand Archaeological Association (NZAA) has its records, and Whanganui's District Plan has others. The two don't mesh very well.
Back in the "bad old days", archaeology was a kind of treasure hunting. Museums used to pay for the excavation of sites they hoped would turn up objects to exhibit. Canterbury Museum excavated the Wairau Bar, a very early Māori site near Blenheim, for that purpose.
These days archaeology in New Zealand is about managing a cultural resource. It involves identifying sites, protecting them where possible and, if they are going to be destroyed, investigating them to get information before it's lost.
Excavations run in two streams, and each needs an archaeological authority from HNZ. Academic archaeologists dig sites they choose for scientific purposes - usually one or two a year. The results are recorded in journals and scientific papers, and relatively well known.
Commercial and consultant archaeologists like David mainly excavate for "rescue" - when a site is going to be destroyed by development. It's what happened at the Victoria Ave/St Hill St site in Whanganui to make space for the new Farmers building.
David was involved in the aftermath, helping move artefacts when the building they were stored in was about to be demolished, then shipping them off to Dunedin later.
"A bunch of us HNZ archaeologists came up and boxed them all up and moved them out."
Information from digs done by commercial archaeologists is recorded in reports, but these are only available in the HNZ online library. This "grey literature" is interesting and freely available and David would like it better used.
"There are 6211 archaeological reports there that people can go and read, and people don't know they exist. There's one on Richard Taylor's house site, one on South Beach and one on Rapanui Rd," he said.