Need some pointers on database scheme

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ASP.NET

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

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.