One possibility is:
System -> Setup -> QlikView Servers -> MyServer
snd in the right hand pane choose Performance tab.
Under the Document section there is Object Calculation Time Limit
Set this to something more strict like 10 seconds. Then if a user creates a bad object QlikView Server will stop trying to calculate it after 10 seconds. If it times out the chart on the user's screen will show 'Calculation Timed Out'.
At least here you are protecting the server and other user sessions from run away CPU use, and memory use.