A couple dogs might help, if you know what you are doing.
This. A bunch of noisy, easily startled farm birds would help as well, in more ways than one.

I'd also consider a home security sign, you may not have a alarm system but a potential intruder doesn't need to know that.
"Beware of Dog" signs are good too, not as good as a barking dog but they don't require any maintenance.
You do realize sign fraud puts countless lives and properties around the world at risk, don't you? Just checking.