*There is a sandbox yes, see Wikipedia: Sandbox. I would not reccommend that you use this to work on new articles, as it's reset fairly often. Instead, start a temporary article in your own userspace, for example  and write up a new section. When you feel that it's complete, link to it on the talkpage of the full article and ask for opinions and feedback. Do not insert it straight into the article without discussion, as this will only result in it being removed as well as aggravating others.  
 :There are no mechanisms to stop any groups from "planting" editors, or to stop biased editors; but usually biased edits will be noticed, reverted and the author notified. If they persist, it may or may not result in them being blocked for various periods of time, or in severe cases for ever. If you take a look at some of the links listed in the welcoming message you should be able to see the various policies we have to keep Wikipedia as unbiased as possible.   -