Your first step when seeking permission to metal detect in parks should always be to contact the park ranger or park supervisor. These people can give you any information you need to seek permission to detect in their parks. Some state parks allow metal detecting, while others strictly forbid the activity.  You should speak to the park ranger before you ever start detecting to make sure you are okay to detect. Some city and county parks require permits and others are off limits. Again, make sure you contact the park supervisor to determine whether you can legally metal detect and what areas are off limits.  For private property, make sure you receive written permission from the landowner. You can get verbal permission, but you are always safer legally when you receive written permission. This way, the landowner and authorities cannot come back on you for trespassing or taking items off the property.