You can achieve the desired effect by following these steps:
1. Handle the client event OnClientDragEnd
of the RadDock control. This event is fired on drag end of the dock controls and it will allow you to detect whether a RadDock is dropped in the right RadDockZone.
2. When a RadDock is placed in the right RadDockZone, you can use the dock's Client API in order to disable its dragging functionality if you want to prevent its movement at all or set the other RadDockZones as forbidden zones so that the dock control can be docked only in the right dock zone.
For your convenience I have created a sample that demonstrates the suggested approach. Please use it as a reference for incorporating this feature into your actual project.
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