Priority encoding transmission is an efficient forward error correction system for the robust transmission of scalable image and video data over packet erasure networks. For a memoryless packet erasure channel we first study the sensitivity of an optimal protection solution to a change in the packet erasure rate and in the number of packets. We then propose a practical error protection algorithm for multicasting and broadcasting applications. Instead of computing an optimal solution for each client independently, we show that comparable results can be obtained much faster by refining protections already computed for other clients. We also consider the situation where clients share a bottleneck link and develop layered multiple description codes that provide a better quality trade-off among all clients than previous solutions.