In my campaign, one of the ways gnomes hide is through geography. Roads subtly curve around hills that are just high enough to hide smoke, strands of trees -- planted decades or centuries ago -- screen views and muffle sounds. Settlements are built into hidden glacial valleys high atop "impassible" mountains. Most passersby don't realize they've just been in the vicinity of a gnomish settlement, because the easy, natural path makes them walk straight past it, without knowing anything was there.
There's no reason that halfling rangers and druids, over the course of many generations, wouldn't be using the same techniques, especially since they only rely on forethought and long lifespans, and not magic.