My back 6 is Shaw, Rance, Higgins, Ibbotson, Hodge & Simpson.
I was apprehensive on Hodge for a long time, and got burned by Ibbo last year (but Johnson our made him too appealing) but these guys picked themsleves (with timing and price changes for my team).
Never really considered McDonald, he's had a really good year but I very rarey get on someone having a break out year because I am doubtful they can keep it up. Of course this means I miss out on a few guys like Jaench and Swallow last year.
I think to close the year out the best 6 defenders will be Shaw, Hodge, Ibbotson then daylight and a bucket of 4-6 players making up the last 3 such as Murphy, Enright, Laird, Higgins, Houli maybe even Newnes... Just my take anyways.
It's been such a fiddly year with defenders that I've gone about trying to get value rather than the best averaging/scoring players at the time.