With WDM networks, the failure of a single link or component may cause the simultaneous failure of several optical channels, potentially making impossible the restoration by rerouting in higher layers directly using the optical network (SDH, ATM, IP). To address this, we introduce the concept of Design Protection, which aims at making such failure propagations impossible. We present the Disjoint Alternate Path (DAP) algorithm, which places optical channels in order to maximize design protection. We show the result on the example of the ARPA-2 network.