Show used by and prevent deletion of the smart lists when they are being used as custom columns in the reports

Currently, the used by tab in the Marketo smart list does not show any people performance reports that are using them in the custom columns. SLs used in the custom columns can also be deleted w/o removing the associations from the reports, and this can easily become an issue where-in someone not knowing if the SLs are being used as custom columns in report(s) delete them just by looking at the used by tab of the SLs. It would be of great help if the used by also showed the people performance reports and prevented deletion of SLs if they're being used as custom columns in the people performance reports.