Objective 1: Your gear needs to be fully hit-capped. This is not negotiable. Your pet needs 100% hit. A tank that misses is going to cause problems. Hit is carried directly down from a hunter's hit to the pet's hit. This includes Careful Aim bonuses, which will be carried down. But more importantly, if your pet is fully hit-capped, they will also be Expertise and Spell-Hit capped. So, no bad parries or pet spell specials flubbing. And if you don't typically melee a boss from the front, let's just say you don't want a boss to get a parry on you. These changes will only apply in patch 3.2 and later.
Objective 2: Your gear should have
Objective 3: Equip two pieces of Tier-7.5 gear for the +5% pet damage. This is desirable if possible. I did it with spare pieces and stacked stamina in them. Tier-7.0 is okay too. If you can't do it, or would interfere with your main dps set, skip it. Just realize that your pet tank will have a tough time keeping on top of the threat list. Pets are a tough sell in my mind as a MT. Their taunt doesn't work on some bosses. I can make a convincing argument for them as OTs. Not getting the +5% bonus will leave dps sitting on their hands instead of pewpewing what you're tanking.
Objective 4: Get to about 25% crit. You need to keep your pet rolling in focus and keep your talents cascading over each other. Crit is the path. This is most critical for solo and five man content. Ten man and twenty-five man content will provide you with more buffs. For those larger raids you may cut a little of this and focus on Objective 5.
Objective 5: Stack Stamina. Really. The pet needs all the pass-through stamina it can get. Even with Great Stamina, Blood of the Rhino, Wild Hunt, and Endurance Training, it wont feel like enough. What saves pets are the ability to shrug off 75% of AoE damage and their incredible bonuses to incoming heals. They still need to be able to survive normal damage while healers are ... indisposed. And if you're stunned or silenced, chances are about 100% that you can't make your pet do it's emergency tank buttons. All that said, please notice that this is Objective 5. It is not objective 1. You need mitigation and focus and everything in Objectives 1 through 4. Don't make your pet the dumb Feral tank that has 50k health but avoids no damage and drains the healers mana like a whirlpool.
Objective 6: Stack raw Attack Power if/when you've met Objective 4. Otherwise, throw in the Agility. Pets get 22.0% of your Attack Power. Make it count.
Gear is a never-ending voyage. I love it. Gearing for pet-tanking is a whole another world. I hope this helps if you take the plunge.
EDITED TO ADD: If you found this useful, try reading Example Beastmaster Hunter Pet Tanking Gear for Patch 3.2 andPet Tanking Talent Choices.
BTW. I love looking at other hunter's raid screenshots. I was just screwing around in Thursday's Ulduar run and took the above picture. I mentioned it to the officers (two being two of our tanks), but not the rest of the raid. A pally healer was confused by the big red turtle with a big red shield over it. Flash had about 35k health raid buffed. He kicked it up a few notches with Last Stand. And yes, I followed my above Objectives in order. I'm sure I could have gotten him a bit more higher in the health department. The wow's from officers were when he was still around 35k health.