new spell: Cannonade

This is a defensive spell.

Name of Spell: Cannonade
Training Cost (usually in elixir) starting at 15000
Targets: any
Effect Type as normal
Damage Type/Amount (if applicable) 120% of normal damage. +5% range, +10% fire rate.
Training Time 30 mins
Description: cast on a cannon and leave until the next time you are attacked, at which time the spell will trigger ( on troops entering weapon range) adding to the defense of your village for say 60 seconds....
Research/Spell Levels available at level 3
Lab Levl 3

This could also apply to bombards, and archer towers....

Your idea is not fit to be a spell as spell is use for raiding not defending your base.