Note that this article is from the LA Times and isn't specifically about Arizona's border. Along California's border they built far more fencing than we have on Arizona's border. They even built fences through the mountains in California. In Arizona only about 40% of the border is actually fenced. The remainder is either vehicle Normandy-style barriers, which are entirely passable by pedestrians and wildlife, or nothing at all, which is what we have in the Pajarito Mtns northwest of Nogales. With more effective barriers in California and parts of Texas, Arizona had become the zone of choice for crossers.
That said, most of the Arizona people I talk to (ranchers, BP, forest service, Game & Fish and so on) tell me the foot traffic is significantly down from what it used to be. Litter at layup/pickup sites isn't nearly as bad as 3 or 4 years ago. Because new and better fencing in some areas seems to have funneled crossers into areas that weren't as attractive before, some places have experienced little or no decrease in night time foot traffic, but the preponderance of evidence suggests a major overall decrease in Arizona. What remains to be seen is what will happen as the economy picks up. The increased number of BP officers on the ground and improved surveillance techniques are undoubtedly helping, but how long will the US want to fund the effort at current levels when apprehensions remain down?