This is definitly a better suggestion than mine. By reading the warning in the Hacker's Guide that it's not possible to bail out of docking in the BeforeDock() event, I got the impression that it was not possible in the AfterDock() event too. But I now stand corrected :)
>In the Toobar's AfterDock event, place the following:
>IF INLIST(This.DockPosition, 1, 2)
> This.Dock(0)
>ENDIF
>This cause the toolbar to undock immediately when the user tries to dock it on the left or right of the screen.