Maybe I've said this before, but if not:

Do NOT waste your time trying to kill a pet or turret in PvP.

Are you a WAR/MNK that needs to refresh your stacks? Fine. Refresh, then pick a real target.
Do you need to put up/keep up an attack buff (Hot Shot/Straight Shot/BotD)? Sure, go for it, then pick a real target.
Is it almost dead anyways? Fine, get rid of it, then pick a real target.

What's a real target? Perhaps the SMN/SCH/MCH that pet belongs to. If there's a pet/turret attacking you, there's an owner close enough to have it there. Attack THEM instead. We can resummon our pets/turrets faster than you can kill them. And you can bet we're already targeting you while you go to town on it. . .

Be smart. Do NOT waste your time trying to kill a pet/turret in PvP.