New to the team: None
Only three players on the Detroit Lions' roster are listed as an offensive guard. One is Rob Sims, the starter at left guard who was acquired last offseason. He played so well that he was given a four-year extension in October, so the Lions expect him to be the starter on the left side of the offensive line for years to come. The same sort of goes for Stephen Peterman, the starting right guard. He signed a five-year deal two offseasons ago, and while he wasn't great last year, the hope is that was due to injuries more than anything else.
The only other true guard on the roster right now is Donald Thomas, who was picked up last November after the Dolphins got rid of him. In Miami, Thomas went from being a starter in 2009 to falling out of favor with the coaches in 2010 and was subsequently let go. The Lions added him as a depth signing, and he is expected to compete for a backup spot this offseason.
The players Thomas will be competing with are Dylan Gandy and Dan Gerberry. Both players are listed as centers, but if they needed to shift over to guard they could. Gandy has made the roster the last couple years because he is so versatile, so he will probably go into training camp with the edge once again.
Need going forward?
The Lions could always use an extra offensive lineman or two during camp for depth reasons, so I wouldn't be surprised if an undrafted free agent or a veteran looking to land somewhere (someone like Thomas) end up spending August with the team.