Wow are you people serious? Re-emburse you for the product that is designed and built to have a reset button for emergency purposes helps users recover factory settings in case something happens? Really? EVERY mfr that has a router has this reset button.
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It's not up to DLink nor is it DLinks responsibility on how users handle these routers after they are purchased. Would be like a Car Mfr trying to tell you who can and can not drive your car after you purchased it. Wow.
So heres the deal and brilliant idea, find a place or office room that can be locked where the router can be placed, used and connected and then put a lock on the office door. Maybe tell your GF not to touch the router? Put the router in a ventilated enclosure/cage of some sorts that's lockable? Yes you can open the router up if your careful enough and maybe some how disable the pin hole from being used. I would make disabling the pin hole good enough that you don't cause the in-operation of the router should you need to use the reset button. There is a good reasons why it's there and has 2 uses, factory reset and recover mode. Should you need this, try to make it available to use at some point should you need it.
Honestly, you need to find a good way to prevent people from accessing the physical router, lockable room or closet would be preferred.
Good luck man. WOW.