Were it me, and with a nice light like that, I'd consider putting a lock-nut on the bolt on the inside of the rack mount, if you have the space for it.
Or even a half nut if space is tight.
Thanks - these are rack mounts that go into the seat stay, so that’s not really an option. But this isn’t a set up for being left locked up outside for extended periods.
Forgive me, but my thinking about using a locknut was more to do with preventing the bolt from unscrewing itself during use, rather than scrote protection.
Like the one illustrated here - albeit, it hasn't been tightened, and is on the opposite side of the frame to which you are referring.
Were it me, and with a nice light like that, I'd consider putting a lock-nut on the bolt on the inside of the rack mount, if you have the space for it.
Or even a half nut if space is tight.