Using dragons with traps

[CyberGuy]

Well, I have level 3 traps but I cannot use it agains dragons because they always go first so I cannot put the traps before they fly over. Enemy dragons have such high initiative. I have horseman and cannoneers but they don't have as good initiative as enemy necromancer or dragons so I have to endure some loss in the first round if the enemy has necromancer or dragons. I don't have necromancer or dragons yet. I am now on level 20 Mage.

So how do use the traps effectively?