Seems pretty clear to me.
1. Caster rolls the initial check; target(s) roll to resist.
2. Caster records net hits.
3. On each turn (which may be problematic in non-structured time), the target can attempt to resist, again, but now their dice pool suffers a penalty of [Spell Force]
4. Each hit reduces the net hits (recorded in step 2) by 1.
5. Repeat steps 3-4 until the victim reduces net hits to 0 and breaks free or the caster stops sustaining.
The penalty is a good reason to cast at high Force and not just set a Limit with reagents!
And I'm not sure but the target seems like it would need to notice the magic or question the thought in order to occur to try and break free. This might be too strong. But if the compulsion seems like your own thought, it doesn't appear that you'd try to resist it UNLESS you thought that was really out of character for you to think that, or you knew you were being mind-controlled.
Compelling a security guard with a notion of "go ahead and buzz these people through the locked door" is different from "turn around and shoot my partner in the face, then myself." Even if Influence might be a better way to handle the former, Control Thoughts is another option.