If I'm working under the table, can I use a contract?

I am providing a specific service, and I want to make sure I'm excluded from specific responsibilities that may arise with the project that I would advise against or want nothing to do with. I am flagging out (hanging colored ribbons) a right of way for a transmission line to a Cell phone tower. The trees in the ROW will be cut down and harvested. I do not own the land or the trees, I am just being paid to hang flagging. I do not consider myself a business, so I would be working under the table. Can I still have a contract describing what I am and am not responsible for if I'm getting paid under the table? Would it be difficult to set up a legitimate "business" for this project if I make less than $200?