If your a prior service MP (any branch) I would reccomend the 66th SF Squadron at Hanscom AFB. It is an active duty squadron that has an oustanding IMA (Iindividual Mobilization Augmentee) program.
The IMA program allows you (as an individual reservist) to schedule your drills and annual training period. If you have ever been in the reserves you understand how cool this is. You do not attend scheduled "drills" with 100 other reservists, instead you schedule when you will attend (4 shifts a quarter, minimum). You arrive, arm-up, attend guard mount and go to work. You must schedule your annual training, basically any 14 consecutive days you want, and come in and work.
The 66th is an LE squadron. You will enforce MGL Chp 90, respond to alarms, domestics, 911, etc. There are 4 operational flights (A-D) that handle LE patrols and supervision, a K-9 section, an investigations section, a DARE program, a corrections section, a CATM (combat arms training & maintenance) section, and so forth.
Our gates are manned by civilian armed guards, which allows us to concentrate on police work.
They only accept E-4's and above. As an E-4 you are automatically placed in an E-5 position. You need to be a trained and mature member that can manage your own military career.
90% of current IMA's are sworn PO's or federal agents that work in and around the local area.