UNDOCUMENTED migrants are rushing to Mexico's border with Arizona, encouraged by the prospect of a guest-worker programme in the United States and anticipating a toughening of border security that would make a dangerous journey even more perilous.Detentions by the US border patrol in south-central Arizona, the busiest migrant-smuggling area, are up by more than 26 per cent since 1 October - 105,803, compared with 78,024 for the same period last year. Along the entire US- Mexico border, arrests have risen by 9 per cent. Many migrants say they are being encouraged by relatives in the US, who are betting on...