The best defense is to develop and train a large enough jury pool to thwart prosecutors through nullification on gun issues.
How would you go about that? Prosecutors and judges try to use voir dire to eliminate any jurors who are aware of their right to nullify, so unless you educate 99% of the population, enough to make it impossible to impanel a jury without them, you'll have trouble if your idea is that they do this openly. If you educate 10%, and they keep their mouth shut, and don't reveal what they're doing even during deliberations, it might work. But then, they might get thrown out and replaced with the alternate for "refusing to deliberate".