Brett Favre had a heckuva 2009 season leading Minnesota to the NFC Championship game before the Vikings faltered against New Orleans.

But his opponents in the NFC North are busy arming themselves in the event that Favre comes back for more in 2010.

The Detroit Lions and Chicago Bears both roared into the new league year with multiple signings and in both teams’ headline moves included adding firepower to their respective defensive lines.

Chicago adding Julius Peppers was the highest profile signing Friday. He turnstiled the Vikings’ inconsistent left tackle Bryant McKinnie while playing for Carolina against Minnesota late in the 2009 season. And there’s no doubt that when he’s on his game Peppers is one of the league’s most dominant pass rushers.

He doesn’t come with the same kind of character baggage that Albert Haynesworth did when he signed his big buck deal with Washington last year. But Peppers does face questions about his consistency and whether or not he’ll keep his level of play up after cashing in on his deal with the Bears. Still it would seem to be a worthy risk for a team that had 35 sacks in 2009 and lacks first and second round draft picks.

The Bears also signed former Viking running back Chester Taylor and blocking tight end Brandon Manumaleuna on the opening day of free agency.

The defensive line was a focus on day one in Detroit as well. The upside offered by defensive end Kyle Vanden Bosch isn’t as high as that offered by Peppers. But Vanden Bosch played with Lions coach Jim Schwartz when the latter was a coordinator in Tennessee. And Vanden Bosch will never be questioned for his effort.

He’ll be heading into his 10th season and he hasn’t been quite as effective the last two seasons as he was when he netted 12 sacks in 2007. But he’s an immediate upgrade for the Lions’ defensive line, which has been atrocious for a long time.

The Lions also added defensive tackle Corey Williams in a trade with Cleveland. Detroit still needs a wide body on the line to snuff out the run better. But Williams was productive with Green Bay as a pass rusher out of the 4-3 before heading to Cleveland, where he was miscast in a 3-4 defense, noted Tom Kowalski, a Lions beat writer for MLive.com, when he was interviewed on NFL Network this afternoon.

In other moves, Detroit dumped defensive tackle Grady Jackson and cornerback Phillip Buchanon (which leaves them without a true cornerback on the roster right now, Kowalski also noted) and added wide receiver Nate Burleson, who can stretch the field and draw coverage away from stud Calvin Johnson.

“They were desperate moves but they were good moves,” Kowalski said on NFL Network. I think he’s right. They may have overpaid for Vanden Bosch and especially Burleson at the current stages of their respective careers. But they weren’t obnoxiously expensive moves. And I think the Lions may have, at least in part, been overspending on veterans with decent character to show other players they are serious about turning the team around.

Both the Bears and especially the Lions, I think, still have a ways to go to catch Minnesota (assuming Favre does return to quarterback for at least another season) and Green Bay. But while it doesn’t say a lot when you’re coming off sub-.500 seasons, both teams are likely substantially better this evening than they were when the day started.