Rigidbody Sync Problem

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Hello,
we have started doing our first game with unity and photon network. We have faced problem with sync. Our main character is ball like sonic. It have rigibody and we did sync for it. Because it is not possible to lock rotation for child objects in unity, we were forced for attributes (like gun for e.g.) make script which follows master (ball). So it is looks like rolling ball with gun next to him. For us is very crucial keep rigidbody on main object. But so far it looks impossible to sync such two objects. Maybe someone did something similar and came up with solution?