Two Sentries with Locker up...both engaging and within 2", with one on each side, of a model without reach:
Can the Locked model move at all?
Nope -- it' can't move.
A Sentry + Warlock also works.
A Sentry + Cyclops Shaman also works.
Just remember locker can only effect jacks and beasts.
I may have no friends, but at least I have Molik Karn!
And remember to align your locker fields well. I Model can be pushed out of locker if you don't cover both approaches.
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or another model will just come up and slam or KD one of the locking models and clean you up.
Sometimes the best strategy to lock up a single beast/jack is just to kill it with the Bronzeback.. :P