You can easily and cheaply prevent this from happening. You can wrap your horn wires with two layers of that corrugated plastic wire loom stuff. If you use two different sizes the larger will fit very nicely over the smaller, and the combination will make it a lot more difficult to clip the wires.
You can also get a short length of small diameter electrical conduit tubing, split it lengthwise, open it up so that it makes a U in cross-section, and safety wire it over your horn wires.
I did both - the plastic loom AND the steel tubing over loom-covered wires. Foolproof and cheap.