I have data in the following format,

A B C D

1 Dept Qty Price Sales (Qty*Price)
2
3

1. I have a formula in column D, how can I use macro to automatically enter
the formula whenever I insert a row, e.g between row 1 and 2. Plus it will
be useful to have the macro update the formula column whenever I add new rows
at the f bottom of the list i.e in row 4.

2. Since this list will be use to enter data I would prefer not to protect
the sheet.
How can I can get macro to rewrite the formula in column D to the bottom of
the list, each time the sheet recalculates, just in case it was accidentally
deleted.