Hello I'm new to asp.net mvc 3 and trying to build my first project which will be a rental site I'm wondering how you would structure it. I have these classes right now

Code:
    public class Member
    {
        public virtual int MemberId { get; set; }
        public virtual int Name { get; set; }
        public virtual List<Rental> Rentals { get; set; }
    }
    public class Movie
    {
        public virtual int MovieId { get; set; }
        public virtual string Name { get; set; }
    }
     public class Rental
    {
        public virtual int RentalId { get; set; }
        public virtual int MovieId { get; set; }
        public virtual int MemberId { get; set; }
        public virtual Member Member { get; set; }
        public DateTime dueDate {get; set;}
        public DateTime startDate { get; set; }
        public DateTime endDate { get; set; }
     }
I'm wondering how you would implement so it wouldn't be possible to rent a movie which is already rented. Right now I can rent a movie and then rent the same movie again. I did a similiar project just in a C# where we checked if the dueDate was null and if it was the movie was rented out.