You will need to create a GTM account and container here: www.google.com/tagmanager/
username: gtm.ClientDomain.com@gmail.com
password: choose-your-password
* = warning: Administrators have the ability to escalate their own permissions!
AnalyticsAgency recommend that all GTM account with delete 
, publish-access 
or manage-user-permissions have 2-stage authentication via sms or iphone app to enhance security.
youtube.com/watch?v=zMabEyrtPRg and support.google.com/accounts/bin/answer.py?answer=180744
Related post here…
