My death knight was never created with the idea of tanking in mind. She was played and leveled unholy till she hit 80 and was basically going to sit there and be my Jewelcrafter and Inscriptionist. I was beating my head on the wall trying to make my warlock “work” in our [hubby and me] Naxx10 run. We had one tank end up committing to tank the other naxx10, and then the second tank was out of guild and just hadn’t made his guild’s run that week and then we had a semi-reliable tank for a couple weeks till he left guild and my hubby was getting particularly frustrated with trying to fill that spot every week, so I suggested we gear up my death knight to fill the spot. I hated my warlock anyway and didn’t give a rip if she got geared by that point.
We got her to 540 defense easily enough. Hubby [protpally] being a maxed blacksmith helped. My dk could also make herself the nice Jewelcrafter gems as well as the tanking ring and necklace. We then looked for ways to increase my mitigation. Rune Strike was a major threat attack and requires dodge/parry-ing an attack. The guild’s other DK tank kept telling me to stack stam and ignore other stats.
Incidently, there seems to be those two schools of thought with regard to gearing tanks – the school of “Moar Stam” and the school of “Balanced Stats”. Hubby came from the “Balanced Stats” school and therefore so did I. Expertise cap  came quickly with gear – no needing to fret over it, though I may have just gotten the “right” gear mix as other dk tanks have told me how insanely hard it is to hit expertise cap. Hit cap  came a bit after that – again, naturally with gear and a couple pieces of gemming.
As hubby puts it, I geared like a paladin [with some focus on dodge/parry mitigation – no block of course :P]. I had less health than slightly lesser geared tanks, but I could also take more hits before going down.
Now I’m at 555 defense [no gems, only head and shoulder tanking chants], 30% dodge, 20% parry, and 10 man raid buffed I’m hitting 42.9k health [over 45k if I use that brewfest 170 stam trinket :P]. So the stam has actually worked itself out with gearing as well 😛
Anyway, in summation, I recommend working on balancing stats rather than putting all your eggs in the “Moar Stam” basket. It’ll mean you have less health to start with, but you’ll be tougher and if you pay attention, and are selective with gear, you can have a better balance overall and problematic stats will sort themselves out, at least for the death knight [I cannot speak for other tanking classes in this regard].