I'd agree that Mienshao is not bulky enough, and you'd want to prolong its use on the battlefield.
Personally, I give it this set:
Item: Choice Scarf
EVs: 252 Atk, 252 Speed, 4 Sp. A
Nature: Naughty/ Lonely
Stone Edge/ Hidden Power Ice
Choice Scarf to outspeed nearly everything (be careful of priority moves); Mienshao is frail so maximise its speed.
Hidden Power Ice is to deal with Landorus; Stone Edge will only do x1 damage and Mienshao will be KO'd, even at full health. If you switch Mienshao out for another Pokemon, it will have to take damage at least once (usually twice) before it can fight back. Besides, switching out to a Water Pokemon will usually alert your opponent.
I only say this because I've had to face one too many Landorus(es). :I