How do you get a super hard nut off of your car's engine mount spacer?

How do you get a super hard nut off of your car's engine mount spacer?
Here are some choices: 1) If it is rusted, tap it gently with a ball ping hammer which will make the rust into dust and allow it to release. 2) Get a butane torch, heat the metal, which will expand the metal and allow it to come off with a wrench. 3) Hit with WD40/CRC/Marvel Mystery Oil or equivalent and allow to sit for at least 15 minutes.Or lastly, sometimes it's just a mater of leverage: get a breaker bar or pipe to put on your rachet/wrench.