On the border beat in County Armagh
On the border beat in in County Armagh - policing is not like anywhere else in the UK.
When I accompanied Sgt Sam Hoey on a drive around his area - we were in a convoy of four armoured cars.
"We're not just worried about the threat for dissident republicans," the experienced officer explains.
"We're also worried about being rammed by other vehicles, and being run over or blocked in places."
On the narrow, single-track roads - where it is difficult for non-locals to know where the border actually is - it is easy to see how police would be vulnerable to anyone who would want to trap them.
As well as dealing with crime which can happen anywhere - such as burglary, domestic violence and drink-driving - the presence of the border means there is a specific threat from organised crime gangs, who are involved in smuggling on either side of the border to
Sgt Hoey's radio crackles with a call-sign, and a colleague informs him of an incident in Flurrybridge, very close to the UK's only land frontier.
"Two boys made off in a van across the border. Windscreen smashed. They've got two boys detained with drugs."
Sgt Hoey points out that is a prime example of co-operation between the Police Service of Northern Ireland and its counterparts in the Irish Republic, An Garda Siochana.
PSNI officers and the Garda are in touch on a cross-border radio, and alert each other when a vehicle they are pursuing crosses from one country into another.
"The reason why we can't cross the border is because we're carrying firearms," Sgt Hoey tells me.
"So if we crossed into the south, we'd be liable for arrest."
Police officers on both sides have numbered codenames for each border crossing point - or "BCPs", as they call them.
"So we'll get a call saying there's a vehicle coming across at BCP 32, for example," says Sgt Hoey.
There are 55 road BCPs in his district alone - and about 270 in total.
Sgt Hoey joined the police as a part-time reservist in 1989, and moved into the regular force a few years later.
He has spent most of his career working near the border - and often reflects on the remarkable change which has taken place.
He points out a hill just outside Newry where there used to be a military watchtower.
He and colleagues would have been flown to and from it by helicopter, or walked to it if there was bad weather.
At the beginning of his time in the police, he did not patrol by car at all.
"The threat was just so high of land mines," he says.
"Two police officers would be walking about with 10 or 12 soldiers."
Over the course of the peace process, the police have spent years building up relationships with communities which had been historically hostile.
In South Armagh, there are still some villages where they "don't get many calls", according to Sgt Hoey - but he can see that gradually changing.
Likewise, the number of signs on lamp posts with messages like "No RUC here" are dwindling.
But signs expressing opinions about Brexit are common sights on our journey.
The messages include "No Hard Border Here," and "Stand Against Brexit."
The PSNI Chief Constable, George Hamilton, and his team of senior officers are examining what the UK's departure from the EU might mean for them.
As well as the impact of any potential changes to the border arrangements - he identifies a general increased focus on identity issues, among both unionists and nationalists, as something which may lead to increased challenges for police.
Mr Hamilton told me: "We just know what it is like policing the volatility of Northern Ireland, and these issues of identity and uncertainty often lead to an increase in tension."
He is employing 102 extra officers between now and the end of this financial year, which is close to the date when the UK is leaving the EU.
But there's likely to be a bid to the government to fund more more - though exactly how many depends on the shape of Brexit.
While he warns that even a Brexit deal would not resolve all the issues for police - because "the terms of that deal may not meet with agreement from everyone" - he also suggests that he'd expect to need more policing resources to deal with the consequences if there was not a deal.
Back on the border beat, Sgt Hoey hopes what he describes as the "massive progress" of the last few years continues.
I'm not a politician, I'm a police officer," he says.
"But small decisions that are made for us can have massive implications for me working along the border."