Whether it be a discussion with one of my Athletes that is a runner or another that is running the marathon as part of an Ironman, our aim is the same. Break the race into four 10K's (and a little). Of course, we are aware of what the athlete can hold based upon the training leading up to the day we're about to discuss. Using this pace as the governor (as opposed to the task master) we aim to jog the first 10K, run easily the second, steadily the third, and comfortably hard (think stand alone 10K RPE)the last. They are encouraged to run as fast as they can the last 2K. Prior to the last 2K, the governor, or goal pace, must not be exceeded.
I emphasize the pace is not a task master. If the athlete must run slower than GP to feel like she's jogging in the first 10K (or whatever RPE she is supposed to for that portion), then she must slow down a little and accept that either she's going to feel better later or that the goal pace has to be reduced a little for that day. Human performance is repeatable to within about 4%... that's more than 16 sec per mile for a 3:00 hr marathoner.
"The Wall" that people talk about having hit has a number of potential culprits, but the first place to look is if the athlete ran too hard early on and simply cracked later as a result. Never (yes, I'm saying never) run faster than goal pace no matter how easy it feels... it's your great fitness, your taper and your enthusiasm conspiring against you.
No matter how you try to sneak up on it... regardless of whether you put plenty of time 'in the bank' early on, you cannot trick or disobey your critical pace curve. As the expression goes, all you can do is all you can do.