On the road in southern Arizona
Nogales, southern Arizona -- Richard Funke and Mike Vyne are both in the same line of business: they try to stop Mexicans illegally crossing the border into the United States.
And, in their different ways, they are both at the centre of one of the most polarising debates in US politics: a debate over a new Arizona law that would force local police officers to check the immigration status of anyone they question in connection with a possible criminal offence.
Here are some numbers for you: population of Arizona, 6.5 million. Estimated number of illegal immigrants in Arizona, 0.5 million. Number of people stopped trying to cross this 30-mile stretch of border illegally last year, 57,000 (that's more than a thousand every week). Quantity of marijuana seized from smugglers, 292,000 pounds, with an estimated street value of $230 million.
There are 2,000 miles of border between the US and Mexico, and the difference in levels of wealth between the people who live on each side of it is said to be the highest of any border in the world. Arizona is the leakiest section of that border - which Richard Funke and his colleagues are trying to do something about.
Mr Funke is a border patrol agent. When he took me out to look at the fence which divides Arizona from Mexico here - and which splits the town of Nogales into two, one bit in the US, the other bit in Mexico - within minutes we watched a young man trying to get through a hole in the fence.
He was quickly spotted by the cameras that monitor the border; agents gave chase, and soon he was sprinting back to the safety of the other side. Another would-be "illegal" stopped.
Mike Vyne doesn't wear a uniform, but he used to. He's a veteran of the Vietnam war, and now leads the Arizona branch of the Minutemen militia, which organises its own border monitoring patrols and reports on any suspicious activity. He insists they do not take the law into their own hands. He proudly accepts the label "militia" (the original Minutemen were a citizen's militia who confronted British colonial forces in the Revolutionary War in the 18th century) - but he draws the line at "vigilantes".
Critics of the new Arizona law say it will enable the police to stop and question anyone who looks Latino. But about a third of the people who live here legally are of Hispanic origin - until the mid-19th century, southern Arizona was part of Mexico - and they resent any suggestion that the police are going to start "racial profiling", in other words questioning people solely on the grounds of their ethnicity.
Its proponents say the new law does no such thing, that in fact it expressly forbids the police from doing so. Here's what it says: "For any lawful contact made by a law enforcement officer ... where reasonable suspicion exists that the person is an alien who is unlawfully present in the United States, a reasonable attempt shall be made, when practicable, to determine the immigration status of that person."
Opinion polls suggest that many more Americans support the Arizona law than oppose it. (Except among Hispanics: two-thirds of them oppose it.) President Obama's attorney-general, Eric Holder, recently met a group of Arizona police chiefs who are themselves opposed to the measure - and he's expected to announce soon whether the Federal government will challenge Arizona in court on the grounds that immigration is not an issue on which individual States are entitled to pass new laws.
But if Arizona gets its way, many more States may follow. Immigration is an explosive issue in the US, as it is in many European countries as well. And southern Arizona is at the sharpest end of the debate. You can hear my report on The World Tonight early next week.