DON'T CUT YOUR ROSS SWITCH!!! The non-derail is simply a small section of completely un-powered "dead" rail which you attach one wire that is connected to one wire on the switch machine.
Good advice above. Go to Ross Page--study diagram. Second, add a small section of track adjacent to Ross switch and use as a dead rail section to activate the turnout machine.
That's why I prefer the set-up of Gargraves switches. These switches are dead from end to end. In others words, power will NOT pass from one end of the switch to the other. This makes it simple to wire the non-derailing function. This is versus Ross where the power passes completely through the switch.