You need a 3 hour layover in ORD because your DFW->ORD flight has a significant chance of being up to 2 hours late. That's just the nature of ORD. Missing an overseas flight may mean being stranded until the next day, since there are not that many overseas flights to any given destination.
Choose shoes and carry-on baggage so that you can run to your connecting gate if necessary.
On the return, if you connect in the US, be sure to book a long enough layover for US immigration and customs, which you will do at the first airport you land at in the US.
Im not so sure if I understand this advice.
The DFW to ORD flight should be just fine. It's the flight leaving from ORD that I'd be worried about. If anything I think one hour layover in ORD is enough, especially since his flight going there is most likely a morning flight so there won't be a back log.
Ideally, he'd also only have minimal carry-on baggage (or none) so that he can run. Maybe that's what you meant.
For the return it is important to have at least 1.5 hours if not 2. The lines can get very long for immigration. Then you will have to pick up the luggage and then go through customs. After customs you will have to re-check the luggage to your next destination. All of that takes time.
Till