Seperation and leaving state with child

My husband is in the military, and I am going to tell him I plan to file for divorce (I know that we must first seperate for 12 months and havee an Agreement in place.)

Here’s the problem >>>

I want to move out of state with our minor son to be closer to family. When we broached the subject of me leaving before, he said the military could transfer him so that he is close to us (which would be OK.) NEITHER of us our NC residents, though we live here now.

QUESTION >>>

How can I ensure that I can leave with our son, as I think that once he understands that I REALLY AM moving, he will play hard ball with me and not allow me to leave.

Must I have the Seperation Agreement say that I can leave, OR should I leave when he is away next time on deployment? I will be dependent upon child support and alimony as well, so this figures into everything.[?]

I have grounds for seperation/divorce, and if I want to play hardball, I could really go after him for FULL custody.

THANK YOU ALL SO MUCH FOR YOUR HELP!!!