Well any pet can be a tank pet now you just have to change their spec from ferocity to tenacity.

I like Quilen for my tanking pets because they can battle rez my other characters and they have a strong defensive cooldown called Stone Armor. When they fall below 40% hp they take 30% less dmg and regen 3% of their hp every 1 sec for 8 sec.

This may or may not be as good as a turtle for tanking but it has battle rez AND a defensive cooldown. This is why i use 5 of them.