Conditional Formatting Ranges are Fragmenting

I have a spreadsheet set up for monitoring my cash flow which uses conditional formatting to warn of impending problems by highlighting cells.

Every time I sort the records, another set of conditional formatting rules is generated using the same formula but applied to a different cell range.  This results in an ever increasing number of rules being applied to fragmented sections of the worksheet and eventually creates a condition where the original purpose of the rule is no longer fulfilled.

How can I lock the range of the conditional formatting rules to prevent them fragmenting?

Regards Tegglet