I wish to grant Manage Permissions permission to all members of my site
so they can secure content. However, I do not want them to go and
change their own permissions to something more privileged.

My thought was I would protect editrole.aspx from being opened by
people without Full Control roles. That way they could still secure
their lists, documents, etc. and they could not change themselves from
Contributor to have Full Control.

I am looking for the best method to go about this and have one idea
that I would like feedback on (and suggestions for implementation).