There are two half marathons at the Detroit marathon. The international starts with the marathon and runs the first half of the course. The us only starts later and runs the 2nd half of the course.
The international half is cool because you get to run over and under the Detroit river. The only downside is the treatment the us border security gives you leaving and returning. I saw a runner get grabbed from behind at the two mile mark approaching the bridge. Granted the runner didn't have his bib displayed on the front of his body, it was on his back. Rules clearly state you need the bib on front and visible when crossing the border. Rules also say you need to bring your passport with you. Anyway, the border guard roughly grabbed this runner, from behind and dragged him off the course. I assume he was allowed to continue after fixing his bib. The way the runner was stopped I think is ridiculous.