How to notch out fence posts so rails are flush with post?
It would take a lot of work to get a clean notch on the posts but it would work. If you are not concerned about the look of the post itself, you could rip the corners of the posts off with a saw at a 45 degree angle with the face of the cut the same width as the face of the cut as the rails, then toe screw or toe nail them in place. It would not be as strong as notching each one in, but it will be much faster. It would be a stronger attachment than just cutting them between the posts. but that is an option as well.