Preventing Cell Change in a Table

So I have this table...
At the bottom of the table the Outer Fences. There is a column at the end of the table that calculates if the value in the row is outside the fences. I tried to do this by using the cell (say, H1500) in the if statement, but as I continued down the column I noticed that row 2 used H1500, row 3 used H1501, row 4 used H1502, and so on. So I have been just entering the new fence numbers as the data changes. Is there a way to go into the if statement and somehow "lock" the cell value so it doesn't change?

Thank you!!