Coax and policies
When I started working at my current place, we had two Ethernet thin coax network running in parallel. One was for TCP/IP, Unix, etc. and I think the other one was for Netware. Among the first thing I did was consolidating both networks into one, it was running much better and was easier to maintain after that.
To reply about rogue DHCP, home routers that florish on the net and so on, we established a policy, that got endorsed by the management and has provision for penalties. When a problem arise, we have the ground to take action. And being a university, with most of the students boarding, the problem arise often, but not only with the students.