Ami,
Looks like it was a breeze for you to get a locker. these days for a small locker the FD required is anywhere between 5lacs, and in chennai lockers are in high demand.
shiji,
Go with your banker, if you maintain an nre account, have some fd's for a 1000 days and get your locker. and the rentals can be paid for 3 years at a stretch.
My banker says there are people who pay for 10 years too to keep the locker.
There are no restrictions. only thing that could restrict are the locker sizes.

you can always file an application for a locker with your banker and check out. sometimes, you could just get one without any of these hassles.