The way in which George has to always look out for Lennie is one way in which Steinbeck is able to present the unequal relationship between both men.
Throughout the course of the novel, Lennie is George's responsibility. As a result, he exerts a great deal of power in the relationship between them. It is his duty to be the "brains" of the operation. At different points in the narrative, George must come up with the plans for both men. In almost every chapter, there are moments when the success of their unequal relationship is dependent on George telling Lennie what to do.
In Chapter 1, George reminds Lennie not to speak when they are interacting with people on the ranch. George's power is continued in Chapter 2 when he has to reprimand Lennie for ogling at Curley's wife because he knows what happened in Weed.
In Chapter 3, George's power is displayed when he controls Lennie's opportunity to fight with Curley, instructing him when to lay off and when to attack. In Chapter 4, Lennie shows some independence in approaching Crooks, but George's power is evident when he orders him to leave Crooks's room. The climax of the novel is the result of what George realizes he must do to save Lennie.
While the situations might change, George's power over Lennie is constant throughout the narrative. Through such a consistent exertion of control, Steinbeck is able to show the unequal nature of the relationship between George and Lennie.