Disable/Enable Yum Update

Hi Team

We setup and use RHEL 6.4 in a stand alone environment. We have got quiet few standalone servers running RHEL 6.4

After registering the server with the RHN, We usually run yum update to ensure that server is updated with all the packages. Once that is done, we would like to stop anyone(even root)from running the yum update command from the Server.

Could someone let me know how is it possible to disable the yum update and enable it back when it is required?

Looking forward for some assistance from the community

Regards
Jo