As of now there isn't exactly much of a good counter against rockets.
Mines can be destroyed by the machine gun and the machine gun can be avoided by driving an other line as the enemy though.
I think that the Quaker and/or EMP (depending on how the EMP works) could pick up that job as there isn't much you can do against the hailstorm of rockets showering down onto you when you are first right now. Mines could detonate when rockets get close to them, resulting in both of them being destroyed.
Yes you can use the shield but there are far more rockets than shields and i think shields should be the last line of defence.
Many people might think that there are too many Assassins, but i don't think so, as they put the first player under permanent pressure. Keeping the amount of them that high but making them counterable (is that a word? ) would force the first player to not take the fastest route but rather pick the one that has enough items to counter the hailstorm.
It would add more strategy to itemusage and raise the skill ceiling, as the player must also focus on using items at proper time and space.