I remember doing cable upgrades at a chain mall in the Vancouver region. One of the problems we had to deal with was tracing back wire in the conduit back to switch from various display stands in concrete. It was a old token ring setup and we had to use the old token ring conduit to run a start cat5 ethernet setup. Can you imagine the headaches how this would be accomplished? I was very good at going into the parking lot, sitting on a ladder, then using a two way FMS radio to call to my partner on the first floor to do mini tugs on the existing cable, and see which junction box it was located in. Better yet, My ladder was parked right in the middle of traffic flow in the garage. A little adrenalin to see how close a moving car gets to my ladder before I jump
Finding a way to trace the conduit pipe in concrete would have really cut down on the tracing of the junction boxes.