OK, thanks for all the suggestions. Clear and box all of the territory where my trains go would be a huge undertaking. i will need thousands and thousands of turrets and walls - just to protect my power poles... the good thing is that it will be safe inside the borders. to produce independent power ...
i have a very annoying problem with the biters always eating my big power poles along the railway. This happens very regularly when they start an attack in bulk, then 1 biter get stuck by a power pole, he starts attacking it until its gone - and it doesn't matter if the way is free 1-2 seconds later...