I've been in the vicinity before - the secret service used analog, but REALLY low power, so you couldn't hear it very far away.
They (secret service) are using a repeater on 165.375 in P25 encrypted tonight.
Looks like they are staying in Sheraton downtown (sidewalks barricaded). I heard a rumor there was a block of 50 rooms bought out...looks like windows covered on top floor.
There were a few units in P25 clear...still about 90% encrypted though...I thought I heard analog DES encryption on one of the low-band fed channels (scanner started again before I had a chance to see freq).
Outer perimeter is controlled by Oklahoma City Police Department, Oklahoma Highway Patrol and Oklahoma County Sheriff's Office. OCSO is broadcasting their stuff on 460.3750 (OCSO Ch 5), dunno about the others.