Can I restrict my Administrators, Domain Admins or Enterprise Admins without a Delegation Model in place?

No. Once a user becomes member of a high privileged group, there is no technical restriction. Because of this, she or him can create/change/delete any other administrator. This is the problem with big AD implementations, which did not consider a proper Delegation model (or a 3rd party tool which might provide this functionality).

Restricting Privileged Users is not possible. This is by Active Directory design.

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