A locked gate and a fence are a good first line of defense. When somebody does drive up my driveway, I go up to them and find out what they are doing on my land, and make it very obvious that I'm taking down their license plate number or lately I just take a picture of it with my phone. Then I listen to their story. Most seem to be just nosy and wanting to see what's going on here. Others tell obvious lies, like they are looking for their friend who used to live here, or they lost a dog, but then don't know what breed it is or what it looks like. I cant say how many where looking for something to steal, most looked like respectable people, but a few had that tweeker look to them that made me wonder.
Our next line of defense are two very large, very loud and very aggressive American Akita's.
I have lights on my buildings that are on all night. I feel that most thieves are cowards and they do not want to be seen. Lights on at night time discourages them.
And of course, we are all armed and we have a lot of experience shooting things