You might try some Loctite 222 (purple) or 242 (blue). Barnett's suggests that this will help seal out dirt, reduce creaking and not increase the removal force. Just be sure to clean all of the grease off first and then wait for it to set up before riding (they say 24 hours).

I've been using the blue loctite on my square taper cranks for several years now and they have not loosened and have not been difficult to remove. It will take a little more work to clean the cranks and bb the next time you overhaul them.

Barnett's also suggests a stronger version of loctite (RC680) for badly damaged cranks.