I don’t understand this sentence at all. Fuera de. Outside of? Went from? Was from? None of these indicate the imperative “get off” to me.
Get off my property means Fuera de mi propiedad (Out of my property). I don’t understand what’s the thing you don’t understand.
The phrase does not look like an imperative at first sight, because it does not have a verb and it lacks exclamation points.
Late to the party, but it’s the equivalent of saying “off my property” in english.