Since I dont' know your exact GPA, this will be a bit generic.
Because graduate school will not factor into you your LSDAS GPA, going to graduate school to improve your chances of admission to law school would really be a very expensive soft factor on your application. Grad school GPAs are heavily inflated and adcoms know this. If you were to get a 4.0 in grad school it would help, but it won't really negate a less-than-stellar UG GPA.
The only way you will really be able to trump or negate a bad GPA is to kill the LSAT. Your service in the Marines will help some (I know, I am a former Marine as well), but because adcoms will focus mainly on numbers, so should be your focus. Don't take the test until you know you are prepared to do very well on it. If you can score well enough, you should be able to get into some very good schools.