DTW airport for Delta is very easy to navigate---there is concourse A and B/C. International arrival will come out at concourse A which will be near the B/C tunnel to walk through. If your Dad can look at the monitors and match his flight number to either the A gate number or the B/C gate number he should have no problem finding it. If he is having problems have him go to any gate with his boarding pass and a Delta representative will surely help him find his gate.