"To hunt rabbits, you need a lot of dogs to defeat the enemies - many warriors, who, having reason, will have no reason to execute their subjects!"
This quote by Ivan the Fourth means that the first option: in order to overcome the quick and furry enemies, it is necessary to drive those who must deal with the fugitives, or with the disguised enemies, the second option about other rulers who kill people living on their land and after they build of themselves white and fluffy rabbits, that is, we must seriously deal with this by sending a letter with many wars, that is, the opinion of that or another ruler of how he rules and acts with his inhabitants.
That's what this quote means.