Do not update formula when inserting rows in Excel

In Excel, I want to be able to insert a row but NOT update a formula referencing that row. For example in Cell B1 I have the formula =AVERAGE(B3:B33) now when I insert a new row at row 3 the formula automatically changes to =AVERAGE(B4:B34) I want to ALWAYS average the rows between 3 and 33.
I have tried absolute values in the formula =AVERAGE($B$3:$B$33) but even they change to =AVERAGE($B$4:$B$34)when I insert a new row.
Any ideas?