Altho the NIFOG is a good set of channels to have, keep in mind that the I is for Interoperability and most FEDERAL events begin within an Agency without the initial need for Interop.
Best to spend time and search 162-174 and 400-420 for Federal activity, which as myself and others have indicated over the years, requires long monitoring, do not expect it to be as busy as your local PD/FD/EMS
Take plenty of notes [Freq, Tones, locations mentioned] and best hint of all - don't share in REAL Time - you don't want to SPOOK the folks into not talking on the radio
Has anyone noticed any Federal activity in the DFW area? I try and monitor all of the NIFOG without any success.