WCF Service exposing DTO or Entity
In general, for DTO purposes you might simply choose not to serialize any "parent" properties. Often, you see DTO with no navigation properties except for strictly associated data (for example, order-header => order-detail, but you wouldn't have order-header => customer - just the customer's key; you'd fetch the customer separately). With this approach, there is a unidirectional path to serialize/deserialize any graph, and it should work fine.