Make sure the job description is to the point and clear
Organisations tend to write job descriptions vague so that the employee cannot turn around with words like "it is not part of my job".
You have to specify exactly what needs to be done by the person at what time. If the job description is not clear enough, change it and ask the person that should do the job to write the detail. Make sure all aspects are covered and let him/her sign it before enforcing it. You can even have a weekly and monthly checklist.
Tip: add a sentence at the end of the job description like " or anything management might require from you." and you wll most probably be covered.
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