Cable ties are a great idea, but they can be easily cut with scissors or a knife.
An alternative I have used in the past is to trim the release tab back to the point where the cable will still latch into the RJ45 port, but the tab is not accessible to release the cable. This then requires a tool to release the tab because its recessed.
Cut at the red line (approximate). You may have to adjust cut location to suit your needs.