jQuery.validate dependancy callback

jQuery.validate dependancy callback

Hi
 
I am trying to do a dependancy call back using JQuery.validate
 
code is
  
fieldsvalue_2: { required: function(element) { return $('#total_travellers').val() >= 2; }, dateISO: function(element) { return $('#total_travellers').val() >= 2; } }
 
It works fine for the required: element but not for dateISO, is it not possible with dateISO or am I doing something wrong..?
If its not a feature, it there any work around that would produce the same result
Any help greatly appreciated.
Kind Regards
Paul Tyson