Spell help

I can't find a spell to base my spell off of.

This is what my spell will do:

well thorns aura has a constants boolean, i dont know about spiked caripus.

this is a spell that you cast onto a target, this isn't an aura.

Base it off any single targeting spell that gives a buff (I think single targetting channel would work). Then trigger this part:

A unit is attacked:

If unit has buff (thorns damage) == true

Deal 3 damage to attacking unit.

Could also be done by adding a modified thorns aura/spikes (as on orc buildings) in a disabled spellbook.

Some time ago I made spell like this. I don't have it but it was requested by Naiden. So catch him on wc3c or wc3anvil and ask for Wind Avatars spell. and yes it was just thorns in spellbook.