Even with public property, there's still the issue of who issues the rules & regulations which are posted at said property. Like the previous poster said, it shouldn't be an issue, in most cases, if the cache is placed with in the guidelines set forth on geocaching.com, there MOST LIKELY won't be an issue. Where you do want to be careful, however, is with places like state parks and gamelands. Quite often, these places have either a specific geocaching policy or regulations for public recreation, which would be inclusive of geocaching. My advice would be to ask. The worst they could say is no!