Lock placement of tables in relationships pane

The ability to 'lock' where tables are manually placed on the relationships pane would be very helpful. We have created a data model with security tables, secured dimensions, unsecured dimensions, and secured fact tables. When I lay out the tables in a specific way, the design is far more understandable than when placement is auto-generated. A 'lock' type of functionality to 'freeze' the table layout would be very helpful because I can more easily locate/verify (a) specific types of tables, (b) bidirectional relationships where they should be (and shouldn't be), and (c) relationship directions are accurate.