Can agencies be prevented from creating the same candidate using different email addresses?

Summary:

Our agencies have been creating the same candidate using different email addresses to bypass any validation that would prevents them, has anyone found this and have you found a way to prevent this?

Is there an easy way to highlight potential candidates that could be duplicaed to the recruiter?

The obvious is tighter legal contractual clauses with them, however the worry is this won't prevent them from doing.

Really interested to know what you or your clients are finding. Thanks

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