Think about the optics you've used in your daily life that have remained in perfect alignment, no matter how many times they've been dropped, worn in a holster, or exposed to the elements. What are they?
I've had good luck with Sig Romeo 5 red and green dot sights (I have 3 of them) as well as a Vortex Spitfire Prism sight. Obviously I use these at relatively short ranges, but they've all held zero and stayed in alignment for me.