If you're going to try a Prot build for Arena then I'd personally go for a deep Prot / Holy build and act as a a kind of combat healer. Prot/Holy got nerfed recently but not to the point of it being completely unworkable - it can be very strong in 2v2. Basically you'd spec Improved Hammer of Justice, use Avenger's Shield to silence, etc but wear PvP Healer Plate and heal away. Having Divine Sacrifice, 30 second HoJ, Avenger's Shield, etc can make you a powerful offensive force as well as a strong and almost unkillable healer.
For gems, I personally go for Spellpower/Resilliance generally. I'm not very experienced at all and I'm only just starting with 2v2 so take anything I say on gems/enchants/gear with a huge grain of salt. Despite my relatively small amount of practice though, I can confirm that a Prot/Holy build in 2s is very fun to play
As far as geming pure STR is the ideal gem basically as you would for ret.
Spec is open to some debate but i use Talent Calculator - World of Warcraft
I'm still playing with it to optimise it but i've been likeing the extra crit i get from the ret tallents but crusade may be a better option.
Read the other post for general idea of gear, enchant for max dps you will have enough survival. Also I would suggest 3s or if you do 2s do it with another dps who can off heal, an ele shammy would be best I think.