Honey pots and canaries are used increasingly now. They, especially the latter, can trigger an alarm once particular segments of an infrastructure are breached or under specific types of attack. However, dedicated honey pots are complex systems and require a lot of set up, maintenance, and monitoring to be of any use and not just liabilities. One way out might be to just scatter some fake SSH keys about the infrastructure and tie them to alarms [kulinacs.com]. The question remains how useful they would be in practice.