Constantly searching is the best experience you can have. When the "balloon goes up" one of the first things that will happen per OOB and COMSEC procedures is that every frequency will be changed.
Frequencies remain the same, unless it is the regular time to change them
I will not be more specific - they change daily at a scheduled time.
In a combat situation - situation of conflict..........they change more often.
There is a book carried by US Military communication personnel with radio frequencies and other information ( like challenge and passwords - but there is a trick to reading them ) - and it is classified as "Secret". When I was overseas in Korea ( 2nd Infantry Division - Camp Casey ), I had a OD green "necklace" that I carried mine in, against my chest...under my uniform blouse. I still have it...packed away, marked on the outside with a permanent marker "Secret". Vetted by my S-2 ( Security ) officer ( Captain ) to carry the "book" in.
There are other ways that the US Military helps guard their land mobile and landline communications. If you are listening in to them......it is because they allow it.
Specifically.........a land mobile radio ( truck mounted & Tactical Operations Centers ) ONCE a U.S. Military Low band radio has been uploaded with encryption.....it becomes a sensitive device. It is not allowed to be "Unguarded". Once it is "Keyed up" an individual with at least a "Secret Security Clearance" has to be near that radio at all times to prevent unauthorized monitoring, and possible sabotage of the radio. So you can see the somewhat of a hassle of "Encrypting" a military low band radio, ( low band "Sincgars" - the radio used in conflicts and wars ) is only done as it is necessary.
FF - Medic !!!