attacking detection

How can I detect how long a unit isn't being attack by spells?

Uh...I'm not sure ecactly what you mean but I'll try anyways. Make a trigger to detect when a ability/spell is finished being casted on your units then start a timer. Now make another trigger for when the unit gets attacked and just check the time between the two with the timer.

YOu can't, cause it is almost impossible to know if damage was caused by a spell or by attack

i don't care if the spell caused damage or not.

So you want to know the time between two spells are cast?

well it's VERY ineffecent and inacurate but you could have a trigger running once a game second and have it increment an integer and have another trigger when the spell is cast, check the integer and reset it to 0.

NOTE: the acuracy of this integer will be HORRID it might be better to run every 5 seconds depending on how long you expect to be between casts.

also you'd need an integer for every unit you want to check...