I'd go further.

I constitutional amendment where one only receives the right to vote after signing up for a term of enlistment. Also no more direct commissioned officers. i. e. someone is only able to qualify for promotion to a commissioned rank until after a min number of years in the enlisted ranks.

And in should not be retroactive (ex post facto) to preserve the rights of us old heads that did not have the chance to life under that contract when we were younger.