Quite simple.

For guys: if you don want other people joke you with a shotgun marriage, then DON'T DO IT. Please do not assume you wont that "lucky" to hit the jackpot. It is not that easy to hit, but once you hit, you are FINISHED.

For girls:
If you want to observe a relationship for future marriage consideration, then DON'T DO IT. Although it cant guarantee your future marriage safe, but it can show how far he can respect you. This kind of approach can "filter" off a lot of buaya which can make you miserable mentally after your marriage.