Building ultra-secure connectivity on existing optical backbones requires more than encryption and key management: targeted physical attacks can still disconnect critical sites. We propose an upgrade planning framework that constructs a physically secure subnetwork among a given set of terminals by selectively hardening intermediate nodes and fibers. The proposed Integer Linear Programming (ILP) formulation enforces K secure paths that are simultaneously link-disjoint and node-disjoint, providing resilience against failures or attacks.