Cheryl, another thought: you may want to consider modifying your workflow. This is actually best practice in geoprocessing tool development (when practical), as any tool that modifies its input 'in-place' is risky because if anything happens during processing (power outage, disk full, user cancel, ghosts in the machine) your data is left in an incomplete state. In my experience this advice especially applies to ModelBuilder which just because of the way it is set up may sometimes compromise stability in its quest to be easy to use. Simpler is definitely better in Model Builder!
Even when working with Python tools, when I have a big complicated process that modifies a workspace in-place, I have set up scripts to copy the data (to a local location, for speed), do a bunch of processing, and only at the end (when we know everything has successfully executed) replace the input with the results. This is still risky, but a little less so.