There are still a lot of unknowns when it comes to long term living on the surface of Mars. The planet has a much weaker magnetosphere than Earth, and so shielding from solar radiation will be needed for any settlements. My guess (and it's only that) is that some type of shielding technology will be soon developed that will offer better protection than what is currently available. It will be lightweight, easily portable, and will probably involve nanotechnology. Great advances are already being made in the development of solar cells, too, and in some cases due to nanotechnology.
As an alternative to above-ground shelters and domed cities, some have proposed living underground (or even growing food underground). One of the areas of interest are the caves found on the slopes of Pavonis Mons and Arsia Mons. The caves are thought to be lava tubes, aka "skylights", and could act as shelters not only from the radiation but from micrometeoroids. Of course this assumes the volcanoes stay dormant. Nearby Olympus Mons already has the distinction of being the tallest mountain on any planet in the Solar System (although it's profile is that of a flat, shield volcano).
The flip side to all of this is that although the caves could be location for a future settlement, they could also act as a hideout. This is a theme I'm exploring in the second and third books of the Chronopticus Chronicles series I'm working on now. More on that later.
Speaking of books, I hope to have the second book in the series, Ionotatron, finished by the end of November...hence I will probably be posting less for a while. The book will build upon the sprawling foundation established in Fractal Standard Time (which is available now in paperback). The e-book version of Fractal Standard Time will also be available by mid-September on Amazon.