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