If some customers at my Internet cafe deliberately break the rules in computing, what should I do?

ces: If some customers at my Internet cafe deliberately break the rules in computing, what should I do?
I formulate rules as guide for customers for smooth and hassle free computing and also to protect my equipment. But some seem to deliberately break the rules or outrightly destroys some equipment. What is the best thing to do?

Answers and Views:

Answer by Ty
System ban their computer from your WIFI.

Answer by Matthew
easiest option is to ban the MAC address from the network and ask them to leave or give them a warning… people will get the message

Answer by Dunbar Pappy ϟϟ
Keep it simple:
WPA-AES encrypt the router, and change password every day; give it out only when customers sign a log book and provide adequate proof of who they are (driver lic., passport, etc.).
Set router to log all activity, and save that to non-networked media for future reference.