No trade secret. I use rustins plasticote two part lacquer and put about 6 coats on leaving it to dry between coats. It is pretty heat resistant, water proof andd alchohol resistant and is used on kitchen worktops. Been using it for some years and no failures yet. I tend to use only harder woods that perhaps don't move as much. Softer woods can move as you say with differences in peoples homes. I also stress that they are for juse ony with cool drinks and not to wash with hot water either.
Pete