You need to pick up points in deflection (+5% parry) in the retribution tree

Sacred Duty (+6% stam) helps as well.

What some/most raiding paladins would do is to drop the holy tree (sadly), and max the +defence and +armor talents as well. Improved judgement is highly recommended too.

http://www.wowhead.com/?talent=sZVhtIx0dMgqtVbx

that's one talent build
you may choose to skip ardent defender , but I think itll be pretty useful , esp/even for multiboxers. alternatively skip spellwarding for reckoning if you want.