Bullets Don't Take Bribes, They Shoot S***

In From the Frontier of Writing, Seamus Heaney develops a conceit in order to show the pressures and dificulties of writing. Heaney develops this conceit through the comparison of writing and the process of writing with images like guns and troops.
There are many ways to interpret exactly what part of the writing process Heaney is writing about, but personally, I think that he is writing about the process of trying to be published. In the sixth stanza Heaney writes "the marksman training down out of the sun upon you like a hawk." I took this as the marksmen being an editor of sorts, just waiting to dive out of the sky and rip your work to shreds. I imagine that this would be a very stressful and difficult time for a writer, having to stand in front of this person who is almost just about playing god with the piece that you've undoubtedly spent quite a while on. And even after you've made it past the editor, you're not out of the woods yet, you still have to walk past "armor-plated vehicles" and "the posted soldiers". These images again show the pressures of trying to be published because even once you've gotten published, the publisher's eyes are still on you, just waiting for your next piece so that they can rip that apart as well.