Why should it be signed when a person is leaving an organisation? It should be a part of the terms of employment when a person is joining and confidentiality clause extended to the period after separation. Or you can make a separate agreement with the employees on a Rs 100/- stamp paper. Usually this is restricted to Managerial cadre.

How far can you exact compliance is the question - seek legal advise on this. And such agreements have to be tailor made for each post/position according to the nature of information etc the person is privy to. A general agreement for all posts can also be made but that will leave too many loop-holes.

Unfortunately I am unable to share our organisational formats with you. We get confidentiality agreements signed by employees the day they join us since breaking of confidentiality is possible even during employment. This agreement covers the period of agreement plus two years post employment. At the time of resignation, a letter is given to the employee reminding him/ her to protect the confidentialy as per the signed agreement.