Slaves, once freed will leave as soon as you enter a new area. I.E the house. You cannot equip them with anything sadly, as I have tried that to make them body guards. But, and Im unsure if this will work, but in theory it plays out.
When summoning anything, if you make the spell 2 seconds+ soultrap for 1 second on target, it makes the creature you summon permanent.
In thoery, you could create a burden 100 points for 2 seconds+ a soul trap on target for 1 second.
Also, command humanoid for 2 seconds+soul trap on target for one second should work as well, to add flavor.
Note: If the spell doesnt work correctly, try looking at your feet, facing the person and casting...if THAT doesnt work, make the spells area effect and make sure they are standing within the area....