From version 0.63b you can specify Minimum Hashrate, and Watchdog functionality
Defaults to 1
-m, –min-hash -1 and upto your maximum hashrate. This command includes multiple features. If set to -1 you will allow the miner to calculate minimum hashrate and set this after while running the miner. Settings this to 0 disables minimum hashrate and watchdog feature. Setting to 1 will enable watchdog feature, and any number above will have watchdog and minimum hashrate enabled.