I don't work, and I am able to save enough of my loan money to cover cost of living and rent over the summer. Most places here only sign 1 year leases, which extend form August 1st-July 29th. I think you would be hard pressed to find a place that would sign a 9 month lease for you hear, which is a shame, where I went to undergrad everyone was willing to do 9 month leases.
I have been in my same apartment since 1st year, and just resigned for my 4th year. Another girl in my class is in my same complex and has been here the entire time too. I would say moving is rare, though there are those students that do move after first year due to unfavorable living arrangements.