How does the network mitigate security risks?

Security and validity of transactions in a sidechain or subchain in a second layer primarily rests with the performance and behavior of the validator nodes. To make sure the validation layer is operating properly, a network first has to have a large number of validator nodes. A small number of nodes in a network is inherently risky and fragile.
In addition and as a requirement for a secure and robust network, it ideally needs to provide for a) the random selection of chain validator sets and b) the rotation of nodes in and out of chains on a frequent basis. Without randomness and rotation, there is a far greater risk of bribery of and/or collusion between validators, vastly reducing the security and integrity of the chains within a network.