Anti-seize, the silver stuff, used for decades in aero engine sparking plugs to ensure succeful removal from the aluminum whilst leaving threads intact. Must admit the WWII plug shells were phosphated (black) steel and would be rusty at first 25 hour maintenance cycle and firmly, permanently in the cylinder head! Modern sparking plugs do have nearly bullet-proof plating.
Threadlocking compound by Loctite claims reduced locking ability up to three removals, if I recall their hype correctly. I always considered that as an emergency back-up idea and just dribbled more stuff on the threads during reassembly.
