Space Invaders - Defense Thing

So simple question, what would be the best way to design the defense bits in space invaders?

I am curious if it should be done using individual little sprites, 6x6, then when they are hit, alter the pixels of that sprite to show the noise/damage effect.

How would you do it?

If for whatever reason you are unaware what I am even on about, have a go and shoot the defense structure:

Space Invaders