You could try banning some of the quick-farming strategies that involve units with no retaliation, but not quick-farming as a whole. Besides, except in rare cases where it gives a significant advantage, it doesn't really matter. Taking hives with 2 Hydras has been the norm for a long time; they're even used in tactical battles, you just need to add some healing. And dragons, at the stage when you have 8 Hydras, don't pose a threat, even in tactical battles.
You could try banning some of the quick-farming strategies that involve units with no retaliation, but not quick-farming as a whole. Besides, except in rare cases where it gives a significant advantage, it doesn't really matter. Taking hives with 2 Hydras has been the norm for a long time; they're even used in tactical battles, you just need to add some healing. And dragons, at the stage when you have 8 Hydras, don't pose a threat, even in tactical battles.