Hills. Which is to say, as long as they still live in the sort of burrows described by Professor T. (which means hillsides) I don't mind if you insist they are close to rivers and bodies of water. When I think of Hill Country I think of either bare, green hills of Ireland/Scotland/Britain or low-mountain sorts of hills - as in Ozark hillbilly kind of hills - either of which I can also see as being halfling country.