[Yaffs] [MLC NAND] How to mark a block bad?

Hello everyone,
Most MLC NAND seem to have the following 2 limitations.
1) A page cannot be overwritten without erasing as Number of Partial
Page Programming (NOP) is 1.
2) Writes within a block should be sequential.
Now how do we mark a block bad when write to a page fails?
This would violate both the rules, as bad block mark is written to 1st
page of the block.
How can we be sure that the bad block mark has been written properly?
Thanks
Rohit