I have never heard of a guaranteed duty station other than an A School assignment out of boot camp. You actually have that in writing that you are going to Alaska, regardless of needs of the service?
I'm editing this to say - I have not, in recent years, heard of guaranteed districts. My son had a guaranteed D1 when he enlisted but that was over 10 years ago. That is virtually non-existent in today's CG. Also, going OCONUS, typically they don't allow married couples straight out of boot camp to go OCONUS. Again, I say this is all TYPICALLY the way it works. There is always occasion for an A TYPICAL situation. I wish you the best of luck.