Suggestions to filter RF from a long wire connected to a logic gate

The following is the schematic of a security system designed to work on the break-wire principle and intended to be used on a perimeter fence. The input 2 of logic gate U-3.1 is kept low via a long thin (60 ft) bifilar wire. Upon breakage of the wire, R4 makes the aforementioned input 1 high, which turns Q2 on. Although I have dedicated filter cap C2 (100nF ceramic) and ferrite bead on the break-wire near the circuit, Do you think that would be enough? Please post your suggestion to improve this filtering and to make this circuit more immune to false alarm induced by RF, EMI etc. The whole circuit board will be placed in an aluminium box except for the break-wire. The power source is 9v battery. Kindest regards

Answer

I would make the tripwire input like this:

^{simulate this circuit – Schematic created using CircuitLab}

This way you keep the low quiescent current but improve the filtering. if the wire breaks.

Also: you can leave out the ferrite bead, it will not help to improve anything.