While messing around looking at old MythBuster stuff on YouTube, I came across this:
Caltrops! Mostly marketed these days for the purpose of discouraging vehicular traffic, although the hollow versions are supposed to be more efficient at deflating tires. However, they’re also handy for deterring foot traffic as well. In conjunction with some ‘tanglefoot‘ wire stringing, there’s the potential to slow someones advance quite thoroughly.
There’s no shortage of commercial sources for the ready made stuff, but sometimes that DIY touch is called for. The easiest way, from what I’ve read, is to get ‘hog wire’ panels and simply cut-n-bend as needed.
Purpose? Well, I’ve seen people attach these things with strings or chain to make an obstacle that is easily laid across a driveway or trail, but can be removed quickly if needed. If I had a place out in the hills and was worried about my privacy, I could very easily see laying some of these across the most likely avenues of approach ‘just in case’. The obvious notion of dumping a bucket of them out the window of your car while being pursued…well, I’m not sure how that would work out but it seems a staple of movies.