Still no Joy validating dates

I have been trying to get the Onvalidate method to work in  a date
field within a dbGrid.

The problem : I have tried to use TRY.... EXCEPT to check whether the
date is a valid one i.e. not 33/22/67. The code I have written for
this never seems to be executed before the Database engine generates
an error - 'not a valid date'.

I have to get this data entry routine bomb-proof as the users have a
habit of typing any old trash in any field.

Do I have the code in the wrong method ?

Or is there another reason that the DBengine gets first look in on the
data ?

Anyone got a novel bombproof date entry in DBgrid code snippet ?
Please ?

Its driving me loopy!