That seems to hinge a lot on having a specific and consistent definition of what "related to the job" and "part of their work" means that won't unfairly affect some companies, maybe there is an established legal definition of that somewhere?
"The test is whether the employer’s actions, and how the employer acted, were what a fair and reasonable employer could have done in all the circumstances at the time the dismissal or action occurred."
How's that for specific and consistent! Yet it still provides protection against capricious firing.