As said before, roses around your property.
In my front yard, I have 2 rows of roses. One shorter towards the front, and one taller towards the rear closer to the front. They look good in bloom, and the neighbors just think they're there for looks.
In the back, on the other side of the fence, I planted cactus. I went to the nursery, and found the prickliest cactus. I actually have 3 kinds back there. It's protection, and its edible.
ON the fence I have a blackberry bush. It exploded with growth, and it's extremely thorny. Someone will have to be extremely desperate to go through the cacti and the blackberry.
I know that plants will not stop someone from coming in. But it WILL control the paths they take and possibly slow them down enough that I have a fighting chance.
I'm actually waiting for my other cactus to "sprout" new growth. I have one tall skinny one that I'm using to grow other ones. It works but its slow. I hate being a cheap ass sometimes haha