Clarification for James Croghan
Like other people have said, it is utterly impossible to police the border in Ireland, and it was never done during the "Troubles" (god I hate that euphemism). The Irish border was hastily drawn up in the 1920's, and was supposed to be redrawn in a border commision that never really happened due to Michael Collin's death in the civil war. The consequence of that is that the border is an absolute rabbit warren network of small country roads used by farmers, with a few major routes. There are roads that pass through NI going from one point in the republic to another without ever joining up with the Northern Ireland road network. There are similar roads going through the republic that are purely for joining up points in Northern Ireland. There are roads that cross the border several times going from one town to another. And those are the main roads. During the troubles, the British army would blow up roads with bombs, and then the local farmers on both sides of the border would dump piles of gravel in the craters to avoid 15 mile tractor journeys to go to fields 1 mile away in farms that straddled the border. Like the original article said, there are towns, villages and even peoples houses that the border runs through. And THOUSANDS of roads.
Of course, in the past both governments were either unwilling and/or uncaring about the border region, and were quite happy to leave it as it was. The result of this was rapid depopulation of the border regions in the republic, and the cutting off from natural markets for business in NI, leading to huge emmigration in Ireland and huge subsidies to Northern Ireland from British taxpayers. I'm glad that the governments are finally seeing sense and encouraging a single economic entity for Ireland (I mean, who gives a crap about nationality within what is effectively a federal European superstate? People want to make $$$, nationality is about local people paying for local services, nothing more). With regards to border controls being put in place between NI and the rest of the UK vs. NI and the republic, which makes more sense? thousands of entry points on an un-policeable border or a few (Dublin, Cork, Shannon, Dundalk, Drogheda, Rosslare, Belfast, Larne, Colraine) entry points to an island?