Direct as last resort

At the risk of annoying the regulars, can anyone enlighten me on how to do the
following...

We have several sibling and two parent caches.
We want the siblings to have priority over the parents
We want the parents to have priority over direct
We want to go direct if the parents have failed.

Why? Cost issues. It is significantly cheaper to go via our uplinks caches than
go direct, however I want to go direct should their caches fail (I don't want
the support calls).

Currently if we use ICP to manage this, the parent caches -always- win (they're
slightly closer and our siblings don't have the same links we do) so that voids
the whole point of having peers.

Turning off ICP for the parents results in the siblings being used but DIRECT
almost always wins when the siblings don't have the object, thus driving up
costs.

Any help appreciated. We're using Squid-2.2STABLE3

Regards,
Antony.

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  Antony Healey         ISOC-AU Founding Member         Ph:  +61 2 9834 6055
  General Manager               & Director              Fax: +61 2 9834 6249
  Healey Communications Australia  --  Giving you the world...
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