Single Unit 'Thorn Aura'

My intentions are simple, I'm seeking for a way to create a somewhat 'Iron Maiden' spell. It's not of course, but I beleive it goes along those lines somewhat.
The Objective is to make an ability that you may attach to a hostile unit, like curse of negative buff. This spell must act like thorns to only a specific unit, so when the unit attacks you, it will take a ' % ,damage of what was dealt. If anybody could help me on this subject, it would be greatly appreciated.

Attempts: Attaching a negative 'Vampiric Aura' to a single unit.

All else fails you could just trigger it use the Damage trigger from the attacked unit.

Thorns Aura with tiny range so it doesn't affect nearby units

Well.. yeah Mr. Apples... Im not sure if you read the whole post or not - judging by your post, it leads me to assume you only read the thread name =P
Anyway, that will affect the Allies of the buff, as far as my knowledge goes, I don't beleive there is a setting for the aura to only affect a single 'hostile' unit. Thanks for the suggestions though,

@ Tim.: Yes, but I want to make sure all other options are considered before I create a code for it.

What are you guys twins or something?

It's not so easy to make a % ability like that, as you'd need some way to detect unit damage, but a specific damage method is pretty easy...
Just buff the unit with a buff that does nothing, and use a trigger to check against when it attacks.

You may need to do some more checks to make sure it's melee somehow, but that's just to make it more like the actual thorns effect.

@ EdwardSwolenToe: No, and I don't see what that has to do with it.

TTFTCUTS: Yes, I knew something like that was possible, but I assume it would require a lot of checks - I was just wondering if there was maybe an alternative. Thanks for your suggestions.

EdwardSwolenToe: We are in the same clan, thats all.

Its a very simple trigger to do actually, without too many checks. I'll explain it next time your on MSN, Joe.

@ Twins: lol you both talk the same, have similar names, avatars and signatures.

Oh sorry, didn't see the cast negative buff part when i read. Too bad there is no give unit a buff function.

Just change the Aura so the only targets it affects is "Self". This doesn't change the thorns effect - it just makes it so only the hero gains the buff.

You didn't read it fully either