Turn on auto hide for taskbar on second screen but not on primary screen in windows 8

Just open task bar properties (right click on it, and select properties). So, you can disable the option "show taskbar on all displays", that will display taskbar only on the primary monitor.

I don't think you can set this in Windows 8 without a 3rd party taskbar manager.

I use DisplayFusion for my multi-monitor needs. It has a feature for adding taskbars to extra monitors in all versions of Windows, and the Taskbar Auto-Hide feature can be set per-monitor.

Perhaps give it a try.

Note: I don't work for them or anything; just a happy user. :)