Mobile, Ala. — Matt Patricia and Cory Undlin worked together for less than a year, but the circumstance and timing of that year set the course of a lifelong bond that has intersected 16 years later in Detroit.

In 2004, Patricia and Undlin were young coaches, in their first year on the bottom rungs of the New England Patriots staff. They were just trying to figure out how to survive and thrive in football.

"You guys know how that goes, we slept in the office together for damn near a year," Undlin said. "When you do that, you get pretty close with people."

Patricia stayed with New England for 14 years, while Undlin followed a far different path. In 2005, he took a job in Cleveland, following Patriots defensive coordinator Romeo Crennel, who the Browns hired as their head coach. Undlin spent the next four years in Cleveland, then moved on to Jacksonville for three seasons, then three in Denver and the past five with the Philadelphia Eagles.

At each stop, the defenses were different. Undlin coached in 3-4 systems in New England, Cleveland and Jacksonville and 4-3 defenses in Denver and Philadelphia, where he coached the defensive backs behind former Lions coach Jim Schwartz's aggressive, attacking front.

Now Patricia is giving Undlin his first opportunity to coordinate a defense.

Since Patricia joined the Lions in 2018, he has preached the importance of a schematically fluid, multiple defenses capable of changing weekly, if needed, to best counter opponents. By adding the schematically versatile Undlin, it offers a chance for Patricia to further realize his vision for the Lions.

"He does have a much different, I would say, experience that I do with defense, that I think will help everybody, from that standpoint, and give us different ideas, different opinions, different philosophies, different techniques, things that will help us," Patricia said."

And like Patricia, Undlin prefers to let his personnel dictate the scheme.

"My overall philosophy would be whatever the players, whoever is on the roster, what's the makeup of the defensive side of the ball, let's do what best fits them," Undlin said. "How are they going to be successful? Let's do that. "

The Lions defense was anything, but successful last season. The unit allowed more than 400 yards and 26 points per game and Undlin's predecessor, Paul Pasqualoni, stepped down from the coordinator position at season's end.

Undlin has yet to dive into his new position. His immediate focus has been preparing for the Senior Bowl, where the Lions are coaching the North team this week. He and Patricia intend to start digging into the roster and scheme as soon as the team returns to Detroit.

"I've got a lot of work to do, as far as getting a great, great feel on everybody," Undlin said. "The evaluation process starts when we get back and we'll deal with that as we go forward through the spring. I can't wait to get my hands on them and start working with them."

The league's collective bargaining agreement will prevent him from talking about football with his new players for a couple more months, but one thing Undlin can say definitively about his defense is he expects passion.

"It's going to be full of guys that play with their hair on fire, that love being out there on every snap, and then guys that know what to do," he said. "That's it, without getting into the scheme aspect of it. And we'll figure out the scheme when we get back there."

One other thing that needs to be sorted out is who will be calling plays on Sundays. Both Undlin and Patricia refuted a report out of Philadelphia that the head coach would be the primary play-caller, but both also declined to add clarity to the situation.

"It's January," Patricia said. "I'm just trying to bring in the people that I think are going to help our players the best. When we get into game plans and schemes, the rest of it, we'll deal with that when we get into it."

jdrogers@detroitnews.com

Twitter: @Justin_Rogers