As insurance against neck warping I put a 1/8 inch x 3/8 inch carbon fiber beam down the center of the neck, under the fingerboard. I route a 1/8 inch slot down the center of the neck early on, and this slot becomes the reference center for all subsequent operations, with 1/8 inch brass pins on jigs so that the neck aligns exactly and repeatedly. Much easier and more accurate than making one edge or the other of the neck the reference. When the neck operations that require the center reference are finished I put in the carbon fiber beam.
The carbon fiber is cut at an angle so it extends all the way into the headstock, reinforcing the joint/angle between the neck and the headstock, a traditionally weak area.
On a Guilele, which has 6 guitar-type strings, I put in 2 carbon fiber beams, and just make some small center routes for the jigs to center on.
Most people seem to use epoxy to glue in the carbon fiber. I have found however that since the carbon fiber is a tight press-fit into the slot, most of the epoxy squeezes out and makes rather much of a mess, both during gluing and clean-up afterwards. I simply press the carbon fiber beam home, which takes a bit of tapping with a hammer. It seats just below the surface of the neck. I then just flood the channel with thin CA glue which wicks into any tiny space or seam and glues things in nicely. Quick, and there is no squeeze-out or mess.