Protecting the cells once the data input is completed

Gentlemen (and madams!),

I am setting up a database with Excel (probably not the best software to do that), and I would like to make it "bulletproof", considering that other people may use it.

It is a file that will be upgraded with additional data from time to time, keeping unmodified the data previously entered. Data will be filled in from row to row (starting from row 1 up to...an indefinite number for the moment). What I would like to do is, once the row has been duly compiled, put a button at the end of the same row to "lock the cells" and avoid any further, accidental or undesired modification.

For example. I have to fill out row#1 : I insert all the data (from column A to column M). I would like to have a button, in cell N1, that once clicked by the operator, locks all the previous cells, from A1 to M1.
Same in row 2, 3, 4... and so on. I guess I have to use a Macro, but I have no idea about hot to set it up.
This way, with the subsequent file access, there is no chance to accidentally modify the previously inputed data. Should we require to manually modify the cell afterwards, we may unlock the file in the normal way (review --> remove protection).

Any idea ?

[EDIT]

Even a floating button, that stands somewhere under the last row compiled, would be perfect....