Not sure my defensive knowledge is all that, unless it is defending the door from a basement escape
I do feel that Gibbs lacks in his defensive nous, but that is symptomatic of modern football. The days of having a Gary Neville style character as your full back are long gone. Look at the side who has won 3 out of the last 4 Champions League titles, they have Marcelo at left back and he has no intention to defend, continually breaks the defensive line to bomb forward and is frequently out of position...but look at what he brings to the attacking side of the game.
When having full backs who are so attack minded, you need the centre backs to factor that in, which I feel is where we have let ourselves down when it has come to Gibbs this season. I look at Evans allowing Lukaku to isolate himself with Gibbs to put that header away earlier in the season as case in point, he should have known where Lukaku was at all times, he was their lone striker and he should have been tough tight to him throughout.
I like Gibbs despite his defensive failings and would like to see him stay on next season, but I would imagine a Premier League club would come in for him during the summer so do not see it happening.