Well, Greg .... that's not quite what I meant by designing for power theft.
One must give them credit for planning ahead, though.
There's only so far you can go with materials and planning. Sure, it helps to use pipe and ru n it in inaccessible places - but I recall one Holmes episode where the thieves core drilled the foundation with surgical precision.
I expect that the final solution would be to have multiple meters, at each end of the line in question. One in the electric room and another at the panel.
As already mentioned, the thief does not always tap his own line. The two power thefts I've encountered involved a tenant tapping into the 'house' power. One of those involved a tap on a branch circuit - so the only means of detection would have been to measure the actual use of that circuit over time.
Circuit layout and identifaction also matters. When a circuit hops all over the place - a common result when the circuit is modified over time - it's just too easy for a circuit to wind up serving multiple tenants as walls get moved about in various remodels. While this may not be deliberate theft, one party pays for the other's use.