Formal/Official:
* Défense d'entrer: This is the most literal and formal translation. It means "defense of entry" and is often seen on signs.
* Entrée interdite: This translates to "entry forbidden" and is also quite formal.
Informal/Casual:
* Interdit d'accès: This means "access forbidden" and is more informal than the other options.
* Ne pas entrer: This translates to "do not enter" and is the most straightforward way to say "keep out."
Other:
* Privé: This means "private" and implies that the area is not for public access.
* Attention, danger! This is used when there is a real danger, and implies that entering could be harmful.
The best translation for "keep out" will depend on the specific situation and the desired tone.