The basic idea was to get 2 Tanking Cooldowns (Boneshield and Lichborne), as well as Anti-Magic Zone, and as many +stamina abilities as possible. The increase in strength also helps in avoiding the melee attacks.
I didn't think this wa spossible, but I guess it is.
Here's a build I just came up with that let's me take 2 tanking CDs at once. With this, I can have a tanking buff up at all times (Icebound Fortitude, Vampiric Blood, and Bone Shield): Talent Calculator - World of Warcraft
Sucks for threat, but you don't need too much threat for tanking Sarth.
This is the EJ 3D build and is the most common build for 3D tanking. You shouldn't have to worry about threat during the duration of the fight and if you want you can have an off tank take Sarth once the 3rd drake dies.
No, there are not typos. I really use just Imp IT in Frost. The napkin math of improving my armor by 15% against magic damage led to... why bother? Even with Bladed Armor, the points just didn't pay off. Note the use of Glyph of RT, as the range is considerably longer than 40 yds. Typically, I have the remainder of the raid tanks put into my group, as they're getting 3.5k heals, based on my needs OR theirs, based on what Grid shows me.
Also, Mark of Blood fills a gap in other method of burning all drakes, then acolytes, as I can pop it during that window to reduce the spike damage on my assigned healers.
While Sartharion does get up to 16k melee hits, I can push 45k health. While a single healer isn't adequate to mitigate that damage, those hits are occuring after all the drakes are down and the fight is strictly against Sarth, blazes and firewalls.