Despite turmoil in the region (Boko Haram was recently active there), only two elephant carcasses were discovered in Yankari in 2015, both of which were presumed to have died of natural causes. That's a big drop from the 10-per-year average prior to 2014.

WCS Nigeria Director Andrew Dunn largely credits Geoffrey, who he says with support from the WCS Nigeria team has thrived in a challenging position.

"Working for WCS in Yankari is not a normal 'job,'" Dunn says. "It requires 24/7 commitment, at a remote isolated site with erratic access to modern facilities. It requires bravery (when Boko Haram threatened Yankari's borders Nacha never flinched) and exceptional levels of dedication, diplomacy, patience, and astute politicking."

Geoffrey has one piece in particular mastered. "I don't really sleep," he says. Instead, he has focused many of his waking hours on raising morale amongst the 100 or so rangers he manages.

In the past, groups of rangers patrolled with few firearms among them, which left them vulnerable to attacks by armed poachers. At least one ranger was killed in 2012. Two in 2013.

Today, they don't go out on their seven-day patrols unless sufficient firearms and ammunition are available and they use intelligence to stay a step ahead of the poachers. Geoffrey also spends at least a night a week in the field with them. "I've tried to get to know them each as individuals," he says, "to understand their strengths and weaknesses."

His work following up on enforcement actions with government officials has also helped ensure that the arrests the rangers make—including 44 poachers last year—aren't for naught.

"Now it's the poachers that are scared," Geoffrey says, "because they know they will go to jail."

Still, risks remain. Just recently, two rangers were shot and injured by arrows from local herdsmen.