Not just with urban exploaration, but on the whole...
If you have a run-in with the police not based on a report or ticket, but because they're suspicious bastards:
-What should you tell/not tell them?
-If they do something you're SURE is against the law, what should/can you do?
-If they assault you without reason, what are your options for defense? Can you mace them or is that still illegal?
-Are there any consequences of catching the incident on tape and reporting it to their superiours/youtubing it and punlicl humiliating them?