That's why the Mars Axle robot is in development. Designed to come attached to a Mars rover, it is extremely simple. It can get to all sorts of areas, and if connected by a cable to its host rover, can even hang off the sides of cliffs to take samples. It's versatile enough to collect all sorts of samples, but it can just reconnect with the main rover for other functions and further travel. It'll hold us over until people get there, at least.