Indeed, being able to specify allowed zones for a given dock seems like a good feature. I will log this feature request in our PITS (Public Issue Tracking System) where you can vote for the feature to be implemented in some of our future releases. If there are many customers that need this functionality (and vote for it) we will consider implementing it.
Here is a link to our PITS: http://www.telerik.com/support/pits.aspx#/public/aspnet-ajax/not-scheduled
For the time being you can use a custom solution. One can be found on the following forum thread: http://www.telerik.com/community/forums/aspnet-ajax/docking/can-i-specify-allowed-zones-for-a-raddock.aspx
the Telerik team
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