I was flummoxed by this very same question several years back when putting rotors onto my new Chris King wheelset. In a moment of desperation that no doubt impaired my judgment, I used a shmear of teflon pipe dope. Worked great, I've not had to touch the rotors since then.
And I dread the day when I have to replace the rotors...cleaning that stuff out will be a PITA. (Unless I just use more pipe dope.)
Dad is sad.
Very, very sad.
He had a bad day.
What a day Dad had!
rotor bolts usually come with a smear of blue thread locker already applied. Just use that if it's present. If they are used bolts then the factory stuff may not be there, just use a drop of blue loctite on each bolt and you'll be fine.