(from the citizensaht.org newsletter)
I have not tried this, but it would be helpful if someone who tried it provide insight on it effect-ability.
The link is to what you need to purchase to make this device. What it does is block the perpetrator ability to see you in your home.
I do not know how effective it is outside though. But if it works inside, this is a start.
It looks like the highest amount you will spend will be about $200 for the combination of materials used to build this device.
Because I have never build this device, I can not say it works. So I should not be held responsible if it does not meet your requirements.