I use a beard trimmer, designed for side burns and facial hair and bought by BF when he had a goaty beard a few years ago, so it's a bit smaller and not as scarry looking as the pic of the one posted earlier.

This keeps things neatly trimmed, but for those hard to reach areas I use a small pair of nail scissors to very carefully trim underneath. This is not a job you can rush ...!

I also use nail scissors if I've forgotten to re-charge the trimmer and just to keep things in check between buzzing.