Several people mentioned it but it bears repeating. BIG HOLES for big plants. Look for good good native soil. Chances are that old soy bean field sitting fallow down the road, just ain't going to cut it ;). The sides of an irrigation ditch in a fallow field is great though. Clearings on edges of woods are usually pretty good spots too. Swamps are great, a LOT of work at the beginning but if you can get a nice mound built up, it's all gravy after that. The side of a river/stream or pond might sound good but all it takes is a kayak or canoe paddling by and it's over. Even some random person hiking or fishing.
Plant 3 patches with this in mind.
1 for thieves
1 for cops
1 for you
Sounds fucked up but............Maybe you'll get lucky, maybe not.
Good Luck
Oh and always go "in" a different way. You might think you're not making a trail but you are. Especially to somebody that's keen to these types things.