You can use the create_unit command to give troops instead of money. More control. And you can keep them in check by building lines of fully garrisoned settlements with high level troops using the create_unit command again. I made a line the went from Kallatis, Tylis, Naissos, up NW to the eastern Alps, across the north Alps settlements. Another point was the Belgae lands, to prevent Germans expanding there too soon and the last one was a line south of the Baltics to stop German expansion to the stepps. Worked very nice in my Roman campaign.