Century/Rajan:
Really? I mean you need someone to help you with this?
In my case, the first time I encountered this problem all I did was change the procedure and circulate it amongst everyone - I changed the HR policy to reflect as 'prior intimation' of leave which explained that if no notice was given prior the shift timing then employee would be marked absent and it took approx. 2 months for employees to change their behavior.
This is not a 'memo' but a policy change that's ideal