I started and built a moderately large DIY spot. It lasted for nearly 2 years before it was destroyed.
Location is key and in most cities it's nearly impossible to find a spot that'll last. The spot we had was an old airport runway, the airport built a new one perpendicular to the old one and the old one had trees surrounding it. It had access from either the airport's parking lot or on the other side in an industrial park and once it got popular people parked in the airport lot and the police caught on.
I'd suggest using google maps to find a location. I've actually started 3 or 4 but they didn't last long, from my experience never build one on anything that's for sale (even if it's been for sale for years). It's probably going to take several tries before you even find someplace that'll last longer than a month.
As far as obstacles, we always just built concrete stuff (boxes, banks, quarter pipes) so it would be harder to throw out, which in hindsight is kind of a douchey thing to do to the property owner. Maybe just built a cheap wooden box or something and see if it will be removed quickly... That'll probably save you money and time in the long run.
You can easily get charges against you too for doing any of this, so be cautious.