When I played Parthia and conqured even some Carthaginians provinces I had all those rvolts quite often so I just garrisoned city with some good cav and some onagers(about 5 cav units and 2 units of onagers)-so in case of revolt I could re-capture city in the same turn it revolted and exterminate population so city stood calm for some turns.So this can be a prof part of a garrison other units may be cheap(peasants for example)just to mantain order.
And if city is rarely revolting better to garrison it with cheap peasants, and have one or two generals in nerby provinces - so it would be possible to hire some mercs in case of enemy's attack.