An old-school coach who prides himself on being a man of principle, Michigan football's new defensive coordinator, Wink Martindale, never considered another option last month before he split apart from his new unit.

His secondary needed to be revamped; something unforeseen when he took the job just a few months ago.

On Thursday, standing under the sun on John Adams Field in Detroit for Sound Mind Sound Body's National Collegiate Showcase at Wayne State, Martindale described how he and new head coach Sherrone Moore shared just a pair of phone calls before the two set a date to meet in person in Ann Arbor.

"By the time I came up to interview, I didn’t know it, but it was pretty much a done deal," Martindale laughed in a conversation with the Free Press. "And I’m really enjoying it."

That's not to say everything's been easy since. Not even that secondary, the crown jewel of the defending national champions, could shield Martindale, Moore and company from the predator that is the transfer portal.

[ MUST LISTEN: Make "Hail Yes!" your go-to Michigan Wolverines podcast, available anywhere you listen to podcasts (Apple, Spotify) ]

U-M's head man had just described the same phenomenon in a conversation with reporters earlier in the day. As he explained, the Wolverines weren't overly aggressive about landing blue chip prospects in the NCAA's online database, rather they staked a fortress around their own who call Schembechler Hall home.

"We had to go for retention," Moore said shortly after he'd finished speaking to hundreds of campers. "There were things that were going on that we had to make sure we kept our core. So for us, we just feel like we're in a good situation at every position to go compete."

HATERATION: Sherrone Moore's message about haters: 'Make their asses suffocate'

While U-M did well to keep most of its team, it wasn't without a miss here and there. Shortly after both of the Wolverines' starting safeties from last year's team in Rod Moore and Makari Paige pledged to return for their senior season, the highly-touted Keon Sabb opted to leave for Alabama. After spring ball ended, cornerback DJ Waller, frequently mentioned as a riser on the depth chart, transferred to Kentucky.

But the real blow had already come, when Rod Moore, who Martindale compared to former All-Pro Eric Weddle after spending time with him in the film room, suffered a knee injury which has since required surgery.

He has operated as a coach in the meantime — defensive backs coach Lamar Morgan said there's no timetable for his return, but it's not entirely ruled out this year — leaving a hole in the back of the defense.

And hence, in the team meeting room shortly after last month's spring game, Martindale shared his decision publicly with the entire defense.

"We want to attack some spots (in the portal)," Martindale said of what he told his players. "We talked to the defense about it before we all left and everything else, and I think we’ve improved our depth."

Four defensive backs in three days

With less than a week before the no-contact period last weekend, U-M added FCS All-American in Aamir Hall. The 6-foot-1, 201-pound defensive back recorded 57 tackles, as well as 15 pass breakups and five interceptions for Albany last season.

Sherrone Moore said there are similarities to the addition of Josh Wallace last year, who paired nicely opposite their future first-round corner and anchor of the secondary, Will Johnson. That would do quite nicely for new defensive backs coach Lamar Morgan, who was also on hand Thursday, and played a key role in re-formatting the defense.

"One thing people don't realize, Aamir played like 950 defensive snaps last year," Morgan explained. "Will Johnson played like 450, so you're talking about a guy that played almost every snap of a season for his team. Whenever you get a guy with that much experience and he wants to move up a level to show people he wants to compete ... I think that's going to add value."

WHO'S STARTING? Michigan depth chart: What the two-deep looks like heading into summer

The next morning, the Wolverines got the news former Tennessee defensive back Wesley Walker was joining the fold. Walker, who Sherrone Moore described as an "experienced, physical, dude (who) loves to tackle and hit," didn't allow a touchdown in 349 coverage snaps last season according to Pro Football Focus.

The now-sixth-year senior also recorded 53 tackles, two bass breakups, one forced fumble and one sack.

But perhaps the most eyebrow-raising move of U-M's portal cycle came when the Wolverines landed Jaden Mangham after he'd spent two years with the rival in East Lansing. He too is a veteran, who logged 53 tackles and led the Spartans with four interceptions to go with three pass breakups and a fumble recovery.

Johnson said he still hasn't met two of the newcomers, Mangham included, but that there's no animosity about coming from MSU; "we just added a running backs coach from Ohio State," he joked.

"Our kids, they invite competition, so they don't really care (where they're from), who's there, as long as they can help, that's all they want," Moore said. "People who will help us win, regardless of who the name is or who the person is."

U-M rounded out its four-man haul the following day with former UNLV DB Ricky Johnson, who tallied 36 tackles and seven pass breakups for the Rebels. While it's not clear if all, any, or none will become starters; the Wolverines wanted to get as many talented bodies in the room as possible, then sort the rest out later.

"That’s the thing, they had 24 or 26 guys and there wasn’t any drop off," Martindale said of how last year's unit became the nation's best. "Matter of fact, some of them played better than the starters at times.

"So that was our big thing, getting back to that."

'The only way you can build relationships is off of honesty'

So did Michigan get back to that? Does it have enough to win a national title?

"You always want more, don't you want more?" Martindale said. "But this game has been and always will be about players. Right now, to answer your question ‘do we have enough?’ We have enough if everybody stays healthy."

Another thing U-M seems to have is an understanding among the players.

In today's fluid environment of college athletics, those in the know say there are widespread symptoms of poor communication; there are plenty of instances around the sport where defensive coordinators didn't call a team meeting to let the roster know how things might shake out, rather they make the decisions they feel need to be made.

That's not to say Martindale is going to run all of his decisions by his players; but he does have an honesty policy.

"I coach these guys just like I’ve coached the pros the last 20 years," he said. "The only way you can build relationships is off of honesty and trust and I’m honest with them. ... It’s the truth. Like Sherrone says, the depth chart is an amoeba, it’s always changing.

"But where I’m different than a lot of coaches, if we’re going to make a switch, I’ll tell the players in front of the entire defense, ‘he’s done this, this and this where as you’re just doing this and this … he’s played better than you right now. So what are you going to do about it?"

There is still plenty to sort out with the defense, which was tops in points allowed and total yards allowed in the country last year. It has to replace a pair of linebackers with nine years of combined experience, work in new position coaches on all three levels as well as a coordinator and, like Martindale said, make sure it stays at least as healthy as last season.

Speaking to players before Johnson's camp later the same afternoon; there appears no sense of complacency. They all know each spot will have to be earned all over again, because it's what Martindale said; and he prides himself on telling the truth.

"It’s coming in the fall," Martindale said, promising a physical style of defense. "We keep it real."

Contact Tony Garcia: apgarcia@freepress.com. Follow him at @realtonygarcia.

This article originally appeared on Detroit Free Press: How Michigan football got Wink Martindale secondary help from portal