Or a small fence? Not tall enough to stop someone from walking over, but enough that it would be damaged by him driving over it. Together with a security camera.

IANAL, nor am I directly citing anything. However, I believe that you cannot willfully setup something with intent to cause damage or harm to people or property that isn't your own.

I believe it's akin to drenching your sandwich with Dave's Insanity Sauce to catch the co-worker who has been stealing your lunch. If your enjoy eating your hot sauce with a side of sandwich, that's fine. It's the intent of how you're using the sauce that matters.

IANAL either, but I think the prohibition is on items that threatan life and saftely rather than trespassers property.

From Wikipedia:

> Mantraps that use deadly force are illegal in the United States, and there have been notable tort law cases where the trespasser has successfully sued the property owner for damages caused by the mantrap. There is also the possibility that such traps could endanger emergency service personnel such as firefighters who must forcefully enter such buildings during emergencies. As noted in the important US court case of Katko v. Briney, "the law has always placed a higher value upon human safety than upon mere rights of property."

Thinking in those terms, a few spike strips on your lawn should be fine.

Unless someone walks across the lawn, steps on a spike, and develops tetanus. The point is it might be legal but you run the risk that it could blow back pretty badly.

Or how about, let's say, a full-concrete birdbath on a column?

He rides over it, blows a tire, his vehicle throws him into the road alongside his usual path, and he is struck and killed by a passing car. I just caused his death and can be criminally charged and civilly sued. Not to mention I don't want to impede regular pedestrians who are welcome to walk along the perimeter of my yard to avoid traffic (there is no sidewalk since it's semi-rural and it's a busy road).

That's exactly the kind of behavior a lawful, civilized society is aiming to prevent.