When Seahawks coach Pete Carroll said in January that he wanted his team to get deeper at linebacker, he wasn't kidding. For the third time this month, the Seahawks signed a free agent linebacker, this time adding Terence Garvin, a four-year veteran who played for three seasons in Pittsburgh before spending last season with Washington.

Garvin, 26, began his career as an undrafted free agent in 2013 and has appeared in 59 games, starting one, while recording 52 tackles.

The Seahawks also signed former Ravens, Jets and Jaguars linebacker Arthur Brown last week, and on Friday they added former 49ers starter Michael Wilhoite. Earlier this offseason, the Seahawks lost backup middle linebacker and special teams standout Brock Coyle in free agency, and Mike Morgan, last year's starting strongside linebacker, is currently a free agent.

"Wilhoite, he played very well last year," Seattle general manager John Schneider told reporters Tuesday at the Annual League Meeting in Phoenix, Arizona. "He's always been a core special teams player for [the 49ers].

"Garvin, really, really tough. Short-area quickness is really good, good instincts, just a guy that we felt like you have to — we're looking at a specific type of person, and both these guys fit that category. We definitely added some toughness at the very least to our special teams."

In addition to signing Garvin, the Seahawks also re-signed exclusive rights free agent linebacker Dewey McDonald. McDonald, who came to the Seahawks via trade last September, quickly established himself as one of Seattle's top special teams players. McDonald finished last season with eight special teams totals, which was second on the team behind cornerback Neiko Thorpe.