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Permits and Clearances

If you start shooting video on open space, a park ranger may require that you have a permit. Whenever you know you're going to be working with a production crew on government land or private property, you first need to gain permission to access areas that are otherwise off-limits or restricted. 

Other places that are off limits to productions unless you get permission first: shopping malls, supermarkets, clinics, recreation centres, public schools.
Sporting events and political conferences may require certain press credentials. Find out out what if any requirements there are and how they apply to your production before you send a crew on location. Better safe than sorry, and you'll be protected from any legal action if a production assistant slips on a cable or gets arrested for trespassing.