Be very careful, that's really the only advice anyone can give you. There's a great video that you can find online called "Never get busted", and it talks about outdoor growing and how to cover your tracks so if the cops find your plants, they don't find YOU, too. Simple things like covering the soles of your shoes with tape so you don't leave footprints (a footprint can convict you), not leaving nute containers or water containers lying around near the grow (fingerprints). Also the way you place your plants can give you away. If you plant more than one, don't put them in neat rows or patterns because plants don't grow this way on their own in nature, and it makes a cannabis grow much easier to spot from the air.
The most important thing to remember is that if the cops find your spot and tear down your plants - don't go back! Take some binoculars with you when you hike out there, and take a look from a few hundred yards or as far away as possible. If your plants look like they've been trashed, just keep on walking and don't ever go back. I know it's tempting to go check on them and see if anything is salvageable, but the cops could be watching for the grower (you) to come back so they can arrest him (you).
Plenty of people get away with growing cannabis right out in the open, but plenty of people get busted, too. Don't be one of those that gets busted!
Good luck