Request: Turret targeting only biters

[PhantomKnight]

Not sure if this already exists, but I would like to see if there is a way to target only biters, and spitters, and leave the bases alone. I saw some posts on the factorio subreddit where someone blockaded the biter bases, preventing from spawning. Trying to blockade them myself, but I'm having difficulties completing the blockade, when I'm working with 7 different bases, at 36% evolution, and spitters and giant biters are showing up to nearly kill me and destroy my pipe blockade. I have Bob's mod mk2 turrets surrounding the whole area, but getting to the middle is near impossible without turrets that don't attack the bases.