In Europe it's very common to have trains stopped (for hours and for the entire community) because robbers stole copper cables. One technical answer to make theft less juicy is to (sadly slowly) replace the copper cables with similar cables but using 1/10th the amount of copper. Another "answer" is a spray, with a chemical compound that has a very specific signature and that's incredibly hard to remove: so the robbers, once caught, cannot deny that they were on scene committing the act: it's not perfect but it makes some of the thieves think twice.