"The people that are making these deals for the government, they should never be allowed to go to work for these companies," Trump said on Fox. "You know, they make a deal like that and two or three years later, you see them working for these big companies that made the deal... they should have a lifetime restriction."
Lifetime sounds excessive to me, but I do think a "cooling off" period should be in order (I'm thinking five years).
However you need to be careful - people in procurement and similar high level Pentagon work need to be treated differently than the people out in the field. It used to be pretty common for people to retire after 20+ years in the military and come to work as engineers and low level managers for companies such as Boeing and LockMart - for the most part the ones I knew were top notch and their real world experience as to how the stuff gets used was priceless.