The phrase "long grass" means that something is not well-known or hidden from people's view. It can also be used to describe someone who is secretive or trying to avoid attention. Full definition
The trailer shows a hunter using various new abilities to take down his prey, including hiding in long grass, distraction, and camouflage. (thesixthaxis.com)
Be sure to keep your dogs out of long grass and areas that could potentially be home to large amounts of ticks. (dogdojo.org)
I tore out long grass for a bed, then stepped through the doorway, a gap in the stones with no walls on either side. (bookbrowse.com)