Free text search and .InField on block property in a page

Having:

public class PageType : PageData
{
   public virtual string DontWannaSearch { get; set; }
   public virtual BlockType BlockProperty { get; set; }
}

public class BlockType : BlockData
{
   public virtual XhtmlString Description { get; set; }     
}

How do I make sure that a search is only performed in fields PageType.Name and PageType.BlockProperty.Description?

Doesn't seem that .InField(x=>x.BlockProperty.Description) helps?

Best regards

Miroslav