I have. It's still not what you think. I've been around the border more than most and I can say that of the times I've been there, there was only one time where I thought I saw somebody hoofing it across the desert. A lot of people don't know it, but just to the west and north of Organ Pipe National Monument, is an air Force testing range. People on foot run the extreme risk of being killed by target practice or unexploded ordinance by walking through there. That shrinks the passable area from the border significantly. So that shifts things to the East of Lukeville and onto relatively flat and open ground until you get to interstate 8, which is roughly 100 miles. I've been all through there at all hours and have never seen anything resembling some massive hoard of people on foot.
Maybe I'm just not looking hard enough.