Its a little more specific than just a defensive D man. This team needs a right handed, semi mobile (not Komi/schenn slow) D man that can play well defensively and make a solid first pass. Doesn't need to be an all star or a guy that puts up points. I would say the best example I can think of is Zbynek Michalek, though he is unavailable, I would assume.
In an ideal world, I would love to get a right handed version of Dan Hamhuis, whoever that is but I doubt we could get anything of the sort, ATM. Our D core would look decent as well:
Phaneuf - RH version of Dan Hamhuis
Gardiner/Gunnar - Holzer
Fraser - Franson