is there a working way to lock slots in a players inventory say just slot 0 in belt 

                     Item c = target.inventory.containerBelt.GetSlot(2);
                      c.LockUnlock(false, target);

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Shows it as locked but still can pull it out of inventory.

This prevents me from throwing it on the ground but not from a player looting it.

You should use hooks to prevent other actions like moving and etc.