Million Dollar Listing LA / NY Series: Prepaid Rental Deals Legit?

[Account Closed]

have noticed in multiple episodes of Million Dollar Listing LA (and possibly NY but i rarely watch that one) that sometimes in marketing the sale of some homes, a rental deal is closed where the renter agrees to prepay the entire lease term (ie, entire 1 year, entire 2 years) up front.

is this legal? or does anything beyond the first months rent in CA count as a refundable security deposit? 

surely an argument can be made that since the lease term is 1 year, prepayment of the whole year fulfills the lease agreement, not 1 month of the lease term and the rest refundable as 'security deposit' in CA, no?