They are described as impossible to stop, so that any civilization that develops them better start using them against everyone or else risk total destruction itself!
I'm brainstorming for ways to defend against RKV. I was thinking that making the orbit of my planets more complicated would make them harder to hit, since it takes some time to accelerate an object to 0.9 c from outside a star system; for this reason if your trajectory is hard to track it gets harder to "aim" the RKV. At the beginning, I thought of making my world a Trojan moon - to add "cycles" to the orbit. Then I thought of replacing my planet with a Bank's Orbital to reduce its profile.
Will adding bodies in a tight configuration (was thinking the hexagonal rosette) help with making the system even more unpredictable, while still providing basic stability?