Now Karachi is a mega polis sprawling hundreds of square miles. The population is about 20 million. The need to move cantonments out of towns can hardly more emphasised. The cantonments are every where and large tracts are occupied. While it is inconvenient for the forces it is also most inconvenient for the people. They can very easily be moved at least 50 km away from the city North West of Karachi. Vast empty areas are available.
Army, Navy and Air Force would also be safe in a lot better place.