Defense against cav army?

How do I counter a really fast cav army?

use tactic with a cat army such as blocking and that cats cant hit cavs going backwards.

use a bigger faster cav army

Can any units attack a retreating unit?

I believe the cat backward cav forward is the only trick of that nature, I don't know other units that can do it

i believe that if your cat speed is enough the same occurs with inf though...

alsoo inf and cavs cant hit retreating archers...

Use your towers and traps upgrade if needed.

Depends what army you use. If you use a catapult army then bring all your catapults + 1 of every other unit. When the cavalry are about to hit your catapults send the 1 unit forward, next turn likewise, next turn likewise, it will stall for time 3 turns where the cavalry will get pummeled. Traps will also stall for time if they are attacking.
Same with an archer army.
Cavalry armies have to be bigger and meaner
Infantry armies... same as cavalry army