One entry per user / Date

One entry per user / Date

Hi All ,

i have 15 fields , one of the fields has a Name Section and the other date , like the following:

Name:
Date:
..
..
.

i want to prevent double entries only when Name and Date are double.
e.g.

Name      Date
John      12-05-2013
John      13-05-2013
John      12-05-2013
 this should be prevented

thank you