There is already a rule of this, the copy/paste rule. But ofcourse there will always sometime happen that someone posts the same resource as someone else, just talk with the guy and provide your thread to him and im sure hell delete it, otherwise provide information with the staff team and theyll for sure help you out, as there is no point in having 2 same resources or more which is an exact copy,
Pretty sure it would be hard to regulate that. Yes it could have the same name but it could be a newer version, completely different reworked version, etc. It would be hard for mods to check every file and see if they are in fact duplicates.