Where at in Indiana?
Find old houses, look presentable, and ask the owners for permission to detect. Don't make a mess, respect their property, and always thank them.
For parks: check their list of rules (usually available online). If it doesn't say anything about not detecting then go for it. DNR controlled property is off-limits. Some people get by with detecting it, but a conservation officer can fine you if caught detecting on the DNR property.