Any soil can be treated to be suitable. The big conditions are sun and avalibility of water. YOU DO NOT WANT TO BE HAULING WATER.
If you are lucky you live close to a river you can use a canoe on--one with lots of overgrown islands. Watch out for the poision ivy in such places. You can get it even from the dried stems of dead plants if you rip them up without gloves on.
Otherwise I suggest you find a stream and get youself some sort of small GPS system. I bought a super sensitive antenna and plug it into my Pocket PC which makes a superior GPS system because you can use a program for driving or one for hiking. I use a program called Memory Map. This way you can just wander along and through a stream and plant a seedling here and there where microconditions are right. Plant them just away from the stream and away from any trails and don't creat a trail to them yourself-- use rocks and fallen logs and such to walk on. Watering two or three times a week should suffice if you set them up correctly. Record a waypoint on your GPS program every time you plant a seedling. This way it will automatically lead you back to them by satellite next time. This way you will not need to plant a field or patch and it won't be visible from the air. If someone finds, or animals eat a few of your plants it won't matter too much as some of them should make it, if you are the least bit competent.
This system is so much more stealth than planting a patch that it's worth the couple hundred bucks to set yourself up with a viable Pocket Pc GPS system. You will also be able to use it as a computer for less intensive activities such as surfing and word processing, listening to mP3, cell phone--etc.
Over a few grows the plants themselves will tell you the best spots to put them. Just be sure to put out a lot of seedlings to start off, and be prepared for some of them to be lost to critters and whatnot, and some of them to flourish. Its amazing how different plants will taste form one area to another, even if they are from the same mamma and all other conditions seem pretty equal. Plus--around harvest time you will not feel as if anyone can rip you of by finding your patch. Someone may get lucky with a plant or too, but if you are stealthy and careful, no one will find them all.
Cheers from the house of mist and fog,