You would have to clear out the abatis/traps/rockfalls/roll-logs before sending in an attack. Also you would have to clear the defending persons fodder (Workers/Warriors/Sword/Pike). After those 2 are cleared the best and most effective way to layer cava/cataph Is : 75kcatap/24996cava/1arch/1scout/1bal/1pult. I wouldn't recommend sending in the bal/pult unless he is with in 5miles.