I just finished a walnut fret board this weekend with CA aka superglue. I cut the fret slots before finishing but next time I will do it after because it makes more sense. I build mostly fretless .
How I do it....sand to a 400 grit finish. Spread CA with a credit card type thing. I use insta-set CA activator but you can just let it dry. I give it 2 coats then sand back flat with 400 wrapped around a block then a quick hit with 600. Next I give a quick rub with 0000 steel wool and finally buff to a high shine with brown paper bag. Sounds like a lot of steps but really takes less than an hour from raw wood completely finished rock hard and mirror smooth.