Requisition email approvals

We are testing the functionnality of approving requisitions via the email notification that is sent and for the most part have it working, one issue that our finance department have with the process is that an aprrover could potentially foward the message on to someone else and they could aprrove the requisition.

Has anybody implemented this and had the same issue if so how did you resolve it.

Thank you,

Stéphane