Texture along Rusty Bars

Hello Blender Artists,

I am making this fan art scene in Blender and I am struggling to get a more random result to the rust on my fence. The bars are all part of the same object (they are extrusions of the upper bar of the fence) and I kinda want the rust to spread randomly along the entire object.

Does anyone know how to achieve this?

Pic for the scene:


Pic for nodes of the fence material:



I kind of mix the black metal with the rust using a grunge texture mask (mask image below, it’s the group in this node I just talked about).

Please, help! Tried everything and nothing worked! The Random output for the node “Object Info” didn’t work at all.

I just wrote this to randomize domino texture lookup, something similar would work fine for this - except: you have to make the poles actual objects or at least dupliverts/duplifaces based (i.e. array or all poles in single mesh won’t work).
Metal: Technically you shouldn’t use diffuse, vary roughness and to some part color (reflection) instead.
Rust: Technically everything has some level of specular reflection, use fresnel to mix diffuse and glossy. Ignore if too expensive to render.

Random from Object Info gives a random number between 0 and 1. Alternatively you can unwrap and position UV islands individually at random locations.