Moving focus from point A to point B perfectly is a trick. A follow focus system with marking disc will help you pinpoint that, but then the dollars start adding up. The old Hose Clamp with a Bolt trick is the dirt cheap way to move a lens, but never seemed like a perfect solution.
How about adding that idea to a rig with hard stops? Here's an interesting rig someone is selling online with a DIY take on getting perfect focus points dialed in for that shot. Not a bad price online either, but a pretty cool idea which i'm sure someone else out there will be able to work with. This throws in some new ideas for that DIY follow focus you've been working on, doesn't it?
DSLR Rig with Follow Focus Hard Stops