Sorry,
I misunderstood the earlier question -
>From the docs:
To enable unicast RPF check, include the unicast-reverse-path statement
at the [edit routing-options forwarding-table] hierarchy level:
[edit] routing-options {
forwarding-table{
unicast-reverse-path (active-paths | feasible-paths);
}
}
yes, the config bits are on the website.... BUT, not the details of the
implementation 
So, does uRPF on a juniper work the same as the cisco??