He's going to be next to impossible to catch in the act. He has found every loop hole.
If you gave his name to every race director he'd just use one of his aliases. Who knows how many he has? (Kip Litton, David Kipling, Rich Rodriquez)
Not every race has displays the entrants publicly. Even if they did, he could use an alias.
Even if they did publicize the entrants, and he wanted to use his real name, he'd still be fine if they had race day registration. (The volunteers handling race day registration are going to have no idea who he is.)
He also cheats on races that aren't marathons. How we really have no idea where he'll strike next?
On top of that, he wears a disguise and sneaks on the course after everyone started. The people most interested in catching him (sub 3hr runners) are long gone by then.
He doesn't stick around for the awards, so he'll be hard to confront after the fact.
It seems like the only evidence we'll have of course cutting is missing splits and missing photos which isn't much to nail him on.
I've run 13 of the races he's either cheated at or is under suspicion of cheating at. Not only that, but I ran similar times to his. 13 RACES AND I'VE NEVER SEEN HIM!
I agree that you need him on video leaving the course and coming back on, but I don't think it's ever going to happen. Some people run with those little spy video cameras and document the race, but they're too busy recording themselves to catch some cheater.
Nobody looks twice when they see someone run off course in a marathon. They know that 99 times out of a 100 it means that someone has a case of the poops. Nobody wants to accidentally witness that.
If he is being monitored, then what is stopping him from faking an injury and dropping out?