Using datePicker to disable dates already selected

hey guys..So I am using datepicker http://www.kelvinluck.com/assets/jquery/datePicker/v2/demo/datePickerStartEnd.htmlto select start and end dates.I have the controller coded so that if the user attempts to select a date from the calendar (which is already stored for them-from a previous selection) it will not add it to the DB. I also have the weekends blocked out so they cant be used (done using
http://www.kelvinluck.com/assets/jquery/datePicker/v2/demo/datePickerCustomCellRender.html)

E.g say the user has previously selected fri 14th and added it to the DB, if they try to make a new record selecting from thur 13th to mon 17th- only thur 13, and mon 17th will be added to the DB. As fri 14th was previously added and 15 and 16th are weekendsone using the following code:
[HttpPost] public ActionResult listHolidays(Holiday holiday, int? PersonId, string HolidayDate, string endDate, string AlreadyExists)
{ DateTime startDates = Convert.ToDateTime(HolidayDate);
DateTime endDates = Convert.ToDateTime(endDate);

while (startDates <= endDates)
{
if (startDates.DayOfWeek != DayOfWeek.Saturday && startDates.DayOfWeek != DayOfWeek.Sunday)
{
ViewBag.CantDuplicateHolidays = String.IsNullOrEmpty(AlreadyExists) ? "date" : "";
var dates = from d in db.Holidays
where d.HolidayDate == startDates && d.PersonId == PersonId
select d;


// <= 0..so if it does not already exist
if (dates.Count() <= 0)
{
Holiday holiday1 = new Holiday();
holiday1.PersonId = PersonId.Value;
holiday1.HolidayDate = startDates;


db.Holidays.AddObject(holiday1);
db.SaveChanges();
//say start date is 10. AddDays(1) will make it 11 then return it to startDates in 'startDates' = startdates,
//but doesnt chage the value of startdates = 'startdates'
}


}


startDates = startDates.AddDays(1);
}


return RedirectToAction("Index");
}
---------------
my view
Date.format = 'dd/m/yyy';
$("#HolidayDate").addClass('date-pick');
$("#endDate").addClass('date-pick');
//$('.date-pick').datePicker//({dateFormat: 'dd-mm-yy'}).val();


// clickInput: true


$(function () {
//3 methods below dont allow user to select weekends
$('.date-pick').datePicker(
{
createButton: false,
renderCallback: function ($td, thisDate, month, year) {
if (thisDate.isWeekend()) {
$td.addClass('weekend');
$td.addClass('disabled');
}


}
}
)


.bind('click',
function () {
$(this).dpDisplay();
this.blur();
return false;
}
)


.bind('dateSelected',
function (e, selectedDate, $td) {
console.log('You selected ' + selectedDate);
}
);


// HolidayDate is start date
$('#HolidayDate').bind('dpClosed',
function (e, selectedDates) {
var d = selectedDates[0];
if (d) {
d = new Date(d);
$('#endDate').dpSetStartDate(d.addDays(0).asString());
}
}
);


//end date is end date
$('#endDate').bind('dpClosed',
function (e, selectedDates) {
var d = selectedDates[0];
if (d) {
d = new Date(d);
$('#HolidayDate').dpSetEndDate(d.addDays(0).asString());
}
}
);
});


can any suggest how to disable a date on the calendar if it is already in the DB