It can be defeated by jamming the relevant frequency bands, i.e. by overlaying other mains recordings with random fluctuations. No deed to remove the original.

It can be defeated by jamming the relevant frequency bands, i.e. by overlaying other mains recordings with random fluctuations. No deed to remove the original. I'm not sure a notch filter would be enough because, even though the mains is supposed to be a perfect sine wave, some harmonics occur (sometimes with a much higher frequency). Perhaps by filtering all harmonics as well? Sound quality isn't exactly a must in these situations. It requires a technically astute criminal, though, and most aren't.