which can transmit for all obstacles
When I was test flying an EC120 at low level in the British Colombia lower mainland I was interested and pleased to experience such a system. As I flew toward a wire span crossing the Fraser River, (I was aware of a few hundred feet up, and high enough to safely clear) none the less, I could hear on the radio, first faint, then strengthening as I approached: "....wires wires wires Wires WIRES WIRES Wires wires wires....". It was transmitted on all aviation frequencies, and was unmistakabe.
Perhaps a temporary recreational wire installation might not warrant such a measure, but probably simple, and maybe justified based upon the perceived risk and flying activity in the area.