We have a crowded computer laboratory. We render free Ethernet ports for laptop users. But they don't carry their Ethernet cables with them, they unplug cable of a fixed desktop PC and plug it to their laptop. When their work is finished, they don't even plug it back to the PC. Worse than that, after a lot of plugging/unplugging, physical damage occurs on the Ethernet ports of the fixed PCs. At the moment, we have three computers whose Ethernet ports are damaged because of this.
How do I prevent people unplugging the Ethernet cables of the fixed machines?