You wouldn’t use the same login as any of your clients, that’s not how you should be using Google Docs (GDs), and it’s uneccessary and WILL compromise security, and trackable editing which are several of the points of a collaborative system like GDs. You’d use your own login (set up a login for each client, and set up a new profile in Chrome for each client too to avoid having to log out/in every time you change which client you’re focussing on) and then share with whoever needs to work on it. Whoever ‘owns’ the document has the power to restrict access and controls who has access to edit etc. It’s no more or less secure than having hte docs in Dropbox (all password protected). The ONLY way it is less secure is if the document is set to ‘everyone can read’ or ‘everyone can edit’ in which case anyone who has the link can either read (without editing), or edit. For example, here’s a link to one of my documents:
docs.google.com/spreadsheets/d/ … 1215732251
Clicking on it will prompt you to request access from the owner (me!) and only after I give you that access will you be able to read and/or edit my document. It’s really very secure!
Additionally, ALL edits are tracked in GoogleDocs and you can review revision by going to File/See revision history. It highlights what’s been changed and by whom and when (I’ve just checked one of my client’s docs, and we have itemised revisions per date/time/person going back to Aug 2014!)
Secure AND roll backable 
Ed
p.s. if anyone wants help setting Chrome up with different profiles and using Google Docs (or comibining the two, please drop me a line, I’m really happy to help… no fees involved, and no ulterior ulterior motives either - promise! 