Found these under google not sure if they work though
http://www.windowscentral.com/how-delay-windows-10-anniversary-update

https://social.technet.microsoft.com/Forums/windows/en-US/2ff2d500-845b-4b1a-afe7-aa52d6c5e57b/how-to-block-windows-10-anniversary-update-1607-via-gpo-or-defer?forum=win10itprosetup

Or......open the start menu, click on settings then update and security, then click on recovery. Where it says 'go back to an earlier build" click on get started.

EDIT: If you have the anniversary update already installed.

in the long term... ... you can't. unless you stay offline permanently

Yes I can. There has to be a way to prevent that update from happening. My computer becomes unusable after that update, too slow. 

Do you still have it installed? If you do then do as I suggested. It won't come back.

I did that, first time windows update ran, it reinstalled it.

You can't stop updates in Windows 10. Pro and up, you can defer, but not permanently.

Damn!