How do you destroy a siege engine in assassins creed revelations den defense

What I've found is the best way to beat a siege engine are certain tactic one of them is for the fire siege, the other for arrow(next step above fire), after these there is a boulder catapult siege which I haven't come up with a working tactic for it yet. For the fire I suggest having a weak barrier in the front and an upgraded barrier in the back so when the front barrier breaks from soldiers or whatever you can trap them between the barriers when you rebuild the weak one. Also put some crossbowmen in the front and back towards between the barriers so they take them out while their suck between the barriers. Now the fire ram will break through all of your defenses but while your crossbowmen are in the front and or middle taking out soldiers I would try to save up as much money as possible without losing your upgraded barrier during the soldier waves so you can put riflemen in the back when be fire tank is attacking your assassin den