Break up the large defence contract companies such as Lockheed Martin, Northrop Gromman and similar companies. This would reduce costs by having more companies compete for large contracts with lower bids than the current monopoly in place now.
Banning high ranking military officers and enlisted from being appointed to any board of any defense contracter for a period of 5 to 10 years following military service. Would limit the amount of influence defence contract companies would be able to have over contract selection, as well as keeping high ranking officers focused on the defence of the country rather than working towards securing a lucrative job following the end of their military career.