If your security model involves stopping root from being root, it is flawed, because it doesn't work that way. You can't stop root from being root. If they really wanted to -- or even by accident -- your root users could write to the disk raw and trash it. There are no restrictions, because that's what root means... And if you do restrict all these somehow, eventually you'll end up in an emergency situation where root needs to do so and can't because you've altered your system in nonstandard ways.

The other problem is that your security model starts from 'default permit'. You wouldn't even write a firewall this way. Are there dangerous commands you don't know about? Almost certainly. Can you weed out 100% of each and every one individually? Doubtful. You need to work from the opposite direction -- give them access to what they need and only what they need, and absolutely nothing more, instead of giving them root, which gives them guaranteed unencumbered access to everything.

You should protect it by not giving out root. Find other ways besides root to let your admins do what they need. You can give them sudo access to particular commands for example without giving them carte blanche.