Defensive spell

I know that most of the spells that we create are used for attacking other players. Wouldn't it be nice to have spells that help protect your village? This spell can be placed over your town hall or over any object that you believe is worth protecting. Here is my idea:

Spell name: Dark Mirror- reflects damage done to the town hall or any chosen object and sends a certain percent back to the attacker. The duration and percent of damage sent back will vary on the spell level. Example: if your "Dark Mirror" spell is level 1, it will reflect 50% of damage back to it's attacker for 10 seconds, leaving the town hall or object unharmed. Each time the spell is upgraded, the damage reflected is increased by 10% and increased by 2 seconds.
Spell Factory level: 3
Cost: 50,000 elixir