remove ability to deactivate wpmu dashboard

Hi,
I intend using wpmu dev for a customer who likes to "tinker".
I would really like him to not be able to inadvertently disable or delete wpmu dev dashboard.

I know I can modify core files in WP to do this but would obviously rather not as changes will be overwritten in any new version update and I would also rather not do it in the theme.

cheers
Ben