How to Mirror a cell on multiple sheets without using a formula

[maclachlan19]

I have 3 sheets, on each of the sheets the user inserts a date in Cell B1.
I need all 3 dates to be the same at all times. So if B1 is changed on Sheet1, it needs to be duplicated on Sheet 2 and 3 in the same B1 cell.
I'm not sure how to do this as I can't use a simple formula because the user is going to be typing over the contents of the cell and the formula would get erased.

 

[JazzSP8]

The easiest way would be to use a formula and then protect the cells with the formula by locking them.

You can choose which cells to protect by right clicking on them and then using Format > Protection.

To enable the lock use the options on the "Review" Tab.

 

[Fluff]

I'm not sure how to do this as I can't use a simple formula because the user is going to be typing over the contents of the cell and the formula would get erased.

Bearing in mind the part I've highlighted in blue.
There is no way that this

I need all 3 dates to be the same at all times.

can be accomplished.
As mentioned by @JazzSP8 the best option is to protect the cell & prevent the user from overwriting it.