Macro/VBA to keep formula in newly inserted row

Ok, here goes:

Here attached is my sample workbook:

Attachment 310920

My button inserts a new row into the table.

What I want is that everytime a new blank row is created, the formula in the Days in Situ column is there as well (but obviously the cells update depending with which ever row it's in.. eg below formula is row 10.).

This is the formula:

=IF(COUNT(G10,H10)=2,H10-G10,"")

I've tried recording a macro that inserts a new row, copies and then pastes the formula, then types in the cells that it applies to. BUT, after a couple of clicks on the button the formulas dissappear. That option doesn't work.

Perhaps it needs some kind of VBA code to ensure that the formula is there in column I....

Can this be done? Major impressed if someone manages to perminently fix this problem!