If you drop down hammer and plead nicely perhaps horseman will spare your life?
Ah ah ah ah ah ! Nice joke.
Most of the horseman are just killhungry, no way they'll spare anyone's life. Even more if it's an archer that can shoot down it's horse.
Back to topic, even the Gk will be amazed by my answer, but... i don't think couching needs any kind of nerf. Sure, there's some really good cav who are able to couch an aware person two second after starting couching, on a hill. But that's just skill. If you start about the "breaking" realism argument, then every weapon will also break after blocking several times, and this will really ruin the gameplay experience.
On another note, i still feel cav being slightly overpowered, thanks to the bumping, but at the moment, i'm more concerned about thoses damn ranged. So be happy Gk, i'll leave the "anti-cav lobbyism" for a while. See you on the battlefield. ;)