Ok, choose which skin you want, I tested this using Inspiration In Glass 2.
Now, since your using ObjectDock Plus, open OD properties > General Tab > Check the option to hide the Windows Taskbar > Click ok. Part of the start button should still be visible, this is where you need to reboot your system. After reboot, log in and the image of the start button should be gone.
I noticed you stated that you, on occasion, would like to use the taskbar. To do this, ignore the above and right-click the taskbar > Properties > check the auto-hide taskbar option. There will still be the image of the start button, again, reboot and log back in.
I have tested both ways and they both worked for me. Explain any further problems.
Links below to Logoff/Shutdown dock icons with included instructions on setting them up if you choose to use the first option.
Link