"Nightline" was with Joiner in Afghanistan, gearing up for another mission: To find and remove all roadside bombs from Highway One, a key thoroughfare that links Afghanistan's two biggest cities: Kabul and Kandahar. As the war winds down, thousands of American troops will rely on this highway for safe passage out of the country.
"They realize that when they get out of that truck," Captain Clinton Winland explains, "Every step could be their last."
As Joiner climbs into an armored vehicle, part of the 20 or so vehicles forming a convoy that will travel several hours on the road, it's easy to think he's crazy -- some kind of adrenaline junkie with a death wish.
But he's about as normal as you can get. On the road, he admits there are days he'd rather be at home, walking the dog and having a barbeque.
"But we've got a job to do out here," he said.
So how does one of the luckiest men in Afghanistan continue to stay alive, even after being blown up seven times?
"Nightline" travelled with Joiner on the mission, where coalition troops discovered a massive, roadside bomb. An explosives disposal team sent in a robot to dismantle it, but before the robot could, the bomb exploded, just meters away from where Joiner stood.
And that was just the beginning.
Find out what happens to Joiner and his unit during their mission in our "Nightline" report.