Sustaining Performance through a flux in Leadership

With change in leadership, the team has renewed focus to prove their worth and a brand new direction to follow. When there is a constant flux in leadership how does one stay focused on making positive contributions ? When there is a new boss every year or every six months, how does a team ensure the culture is preserved and we take a stride forward in the actions taken in the past? As we see the world change today people's interest to stay and sustain is reducing and talent is keen to move forward every 12-18 months. While that is a good practice at the entry level... It is important for organizations to be careful with talent movements especially at a functional lead level. Too many changes can probably do more harm than good for the talent as well as the team. So how do we ensure team members sustain motivation levels and contribute when they see a flux in leadership team level especially during critical times like these?