I second Krill's metal/horses suggestion.
If the copper's going to be on the main donut, what about having each player's copper be radially aligned with their start, give or take a tile or two, just near the inner edge of the donut? That way, they still have copper access (if someone gets beat there...well, that's their fault), but it'll take a relatively far-flung city + road network to connect it.
If the copper's going to be on the main donut, what about having each player's copper be radially aligned with their start, give or take a tile or two, just near the inner edge of the donut? That way, they still have copper access (if someone gets beat there...well, that's their fault), but it'll take a relatively far-flung city + road network to connect it.