The main motive behind the 40-man expanded roster season in September is to either give opportunities to young prospects (i.e Brian Flynn) or for veterans who are looking to return from the DL. Outfielder / third baseman Chris Coghlan is a great example of that second option after rehabbing from a back injury that was suffered in mid-June. During his extended rehab stint in the minors, Coghlan spent a majority of his time at the hot corner which appears to be an experiment that's going to continue as he returns to the Marlins lineup.
Throughout the majority of the season, manager Mike Redmond has used the combo of Placido Polanco and Ed Lucas to man the hot corner. On a team filled with many flaws, that duo has been one of the most flawed positions on this Marlins team. While Polanco has been one of the top defensive third basemen since the turn of the century (three-time Gold Glove winner with Detroit and Philadelphia) but age has deteriorated his skills both offensively (.250/.304/.286) and defensively (-3.6 UZR). Meanwhile, 31 year old Ed Lucas has been the typical replacement level type of player that you would expect from a career-long minor league even though his overall offensive numbers (.236/.300/.301) stack up pretty well with Polanco.
Before he landed on the DL in June, Chris Coghlan was one of the most efficient offensive players in Miami despite a clear lack of power. His .272/.320/.402 line would immediately put Coghlan over that duo but there's a small little problem; he only has seven innings of time at third base in his entire big league career. That would be an issue if the Marlins were actually in a situation in which they had an opportunity to make the postseason which would make every single inning extremely important.
Of course, the team is currently in the complete opposite position where they really have nothing to lose which would be the perfect opportunity for Miami to test Coghlan out at 3rd base. If the Marlins do decide to insert Coghlan at the hot corner, it will most likely be a temporary fit for the next few seasons with 2013 first round pick Colin Moran continuing to look impressive in his short debut season with Low-A Greensboro.
Until we reach the moment in which Moran makes his debut at 3rd with Miami, the Marlins are going to either experiment with Coghlan and hope for the best or go for another route in free agency. As you can see from the following link, the small crop of potential third base is middling at best so it would probably be the best idea to give Coghlan an extended look at the third base position while Moran continues to progress through the farm system.