Secure and Super nodes of ZenCash have performed well to prevent replay attacks.
thanks for adding them to the network, MedaR.
For now Secure Nodes and Super Nodes do not have protecting propose against 51% attack, but with this new redistribution of block rewards 10% Secure Nodes,10% Super Nodes, 10% Treasury, only 70% goes to miners and this significantly reduse chance for this attack.
We are working on solution for this, please read this white paper https://zencash.com/assets/files/A-Penalty-System-for-Delayed-Block-Submission-by-ZenCash.pdf