Please ensure you don't give users the ability to run "ad hoc" queries in a productive environment.
Your statement ...
Sometimes they do crazy things.
... implies that they probably do not know what they are doing. Turning on the Resource Governor in a productive environment could have a negative impact on the production.
Blitz Result: Resource Governor Enabled
If you have to enable the Resource Governor please ensure you read the documentation and understand the implications and impacts this can have.
Resource Governor (2012) (Microsoft MSDN)
The easiest way is to restrict their ability to log in to the server.